Japan Standard Time - history

While the National Institute of Information and Communications Technology was only established in 2004, it is the direct successor of institutions that have worked on the generation and distribution of standard time since the early 20th century.

(Dates are given as dd/mm/yyyy or abbreviated to mm/yyyy as appropriate.)

09/1927 (Showa 2)	Tuning fork multivibrator oscillators purchased from H. W. Sullivan Co., Ltd. in London are installed at the Electrical Testing Laboratory of the Ministry of Communications, and at the Iwatsuki receiving station of the Tokyo Communications Bureau.
11/1927 (Showa 2)	The Ministry of Communications starts the informal broadcast of reference radio signals for calibration of communication stations, transmitted from the Tokyo Communication Bureau's Kamikawa transmission station in Chiba prefecture. The broadcasts are remotely controlled from the Iwatsuki reception station in Saitama prefecture, where the frequency of the emitted radio signal is measured by the tuning fork frequency standard. Corrections are then applied accordingly.
03/1928 (Showa 3)	The tuning fork frequency standard is completed, with a frequency accuracy of 1×10−5. It will be maintained until 1937. The first frequency comparison in Japan is carried out between the Electrical Testing Laboratory, the Army and the Navy, using a crystal resonator. While the initial comparison is unsuccessful, it is repeated nine times until 1937. The lowest achieved uncertainty is 3×10−7.
10/1929 (Showa 4)	Japan's first international frequency comparison is conducted with the German National Institute of Applied Physics, using a luminous quartz resonator purchased from Loewe Radio by the Electrical Laboratory and the Tokyo Central Broadcasting Station. Instead of the multivibrator at the Iwatsuki transmission station, a crystal-controlled standard radio wave generator manufactured by General Electric Co., Ltd. is used, which is calibrated by the Tokyo Observatory.
04/1934 (Showa 9)	The Ministry of Communications purchases a crystal frequency standard from General Radio and installs it at the Iwatsuki receiving station. It is used until 1944, when it is relocated to the Makuhari Standard Radio broadcast station in Chiba prefecture.
1936 (Showa 11)	The crystal frequency standard is completed at the Electrical Testing Laboratory, with an accuracy of 1×10−7.
1937 (Showa 12)	The tuning fork oscillator is replaced by the crystal frequency standard. Construction starts for a standard frequency broadcasting facility at Kemigawa transmitting station of the Tokyo Metropolitan Bureau of Telecommunications.
30/01/1940 (Showa 15)	The official broadcast of standard frequencies is started at the Kemigawa station in Chiba prefecture after installation of the main frequency standard at Iwatsuki receiving station. The carrier frequencies are 4 MHz, 7 MHz, 9 MHz and 13 MHz, each with an output power of 5 kW and a frequency accuracy of 1x10−6. The frequency is calibrated by the time signal of Tokyo Observatory. The signals are modulated at 1 kHz, using a Pierce oscillator of the Electrical Laboratory of Japan, with a Matsumura-cut 100 kHz crystal. The callsigns for these stations are JJY, JJY2, JJY3 and JJY4 in order of frequency.
1943 (Showa 18)	The Ministry of Communications decides to install a main frequency standard at Koganei, close to the Tokyo Astronomical Observatory, as well as a secondary standard for transmissions from the Makuhari broadcasting station.
15/08/1945 (Showa 20)	The standard radio wave broadcast is halted due to the end of the war.
01/04/1946 (Showa 21)	The standard radio wave broadcast is resumed for frequencies of 4 MHz and now 8 MHz from the Kemigawa facility established before the war.
05/12/1946 (Showa 21)	A 12 MHz signal is added to the broadcast, and the output power of each signal is reduced to 2 kW.
04/1948 (Showa 23)	On the occasion of the solar eclipse observed on Rebun island, minute and second signals are added to the standard radio wave broadcast, with very good results.
01/08/1948 (Showa 23)	A report of seconds is added to the standard radio wave signal using a short point method of 0.1 s length. Controlled by the Tokyo Observatory in Mitaka, this reaches an accuracy of 0.03 s. The 12 MHz signal is stopped.
15/12/1948 (Showa 23)	The Ministry of Telecommunications Installation Law is passed, with Article 5 requiring the new ministry to set frequency standards, provide standard radio signals and broadcast standard time.
23/08/1949 (Showa 24)	A standard radio signal at 8 MHz is broadcast from Koganei. The frequency standard is now operated by the Standards Section of the Radio Agency, an external office of the Ministry of Telecommunications. The 4 MHz transmission follows on 20/09, completing the transfer from Kemigawa.
01/11/1949 (Showa 24)	The capability to broadcast a warning message "W" is added to the standard radio signal.
16/12/1949 (Showa 24)	The Standard Station of the Standard Radio division in the Radio department of the Radio Agency is completed in Midoricho, Koganei. This includes the primary standard in addition to the broadcasting facilities. The facility also has a prototype room located 12 m below ground. A new electronic bridge circuit is used for the crystal oscillator, which is now a GT cut. This results in a frequency accuracy of 1x10−7. The activities in Makuhari and Kemigawa end.
1949 (Showa 24)	Production of a 100 kHz GT cut crystal is started for standard radio wave generation.
01/06/1950 (Showa 25)	The Radio Law takes effect.
06/09/1950 (Showa 25)	The capability to broadcast an alarm message "U" is added to the standard radio signal.
10/1950 (Showa 25)	The GT-cut crystal oscillator type 100 achieves Q = 68,000.
01/01/1951 (Showa 26)	The time information format of the standard radio signal is changed to carrier interruption. The 1 kHz modulation is interrupted for 0.02 s at each second, and for 0.2 s at each minute. The time signal source is switched to use Koganei's crystal clock instead of the signal transmitted from Tokyo Observatory.
05/1951 (Showa 26)	The GT-cut crystal oscillator type 200 achieves Q = 150,000 at impedance R = 75 Ω.
28/06/1951 (Showa 26)	A prototype station starts operation with a standard frequency broadcast at 2.5 MHz, 5 MHz and 10 MHz, each with 1 kW output. The call sign is JJY, and in addition to the time and warning messages, and the station code in A2A modulated Morse code, a voice announcement is included from December.
10/1951 (Showa 26)	The GT-cut crystal oscillator type 400 achieves Q = 263,000 at impedance R = 41 Ω.
24/03/1952 (Showa 27)	A new alarm message "N" is added, and the code broadcast for 10 minutes of every hour is changed to "JJY JJY 1640 NNNNN" for both 4 MHz and 8 MHz signals.
01/08/1952 (Showa 27)	The Radio Research Laboratory (RRL) is established as part of the Standards Division of the newly formed Ministry of Posts and Telecommunications. It continues the frequency standards work in Midoricho, Koganei.
10/1952 (Showa 27)	Trials begin for time code transmission by superposition on the carrier frequency in place of the carrier interruption method. Design and production begins for a stable electronic bridge oscillator with a double constant-temperature bath, manufactured by Ando Electronic Co. Ltd.
12/1953 (Showa 28)	The GT-cut crystal oscillator type 700 achieves Q = 450,000.
1953 (Showa 28)	Development starts for a passive atomic frequency standard based on the ammonia 3-3 line.
01/01/1954 (Showa 29)	The prototype station is promoted to become the standard, still broadcasting at 2.5 MHz, 5 MHz and 10 MHz. The accuracy is 0.01 s in time and 2×10−8 in frequency, as recommended by the Consultative Committee on International Radio (CCIR). Time announcements in Japanese and English are added every ten minutes.
1954 (Showa 29)	The new radio wave transmission building is completed, the transmitter is relocated and a new receiver is installed. Development is completed on a new constant temperature bath with a temperature stability of ±1/1000°C.
03/1955 (Showa 30)	A new high-performance generator for the minute-second signal and control signals for the standard radio signal broadcast is completed.
18/06/1955 (Showa 30)	Transmission of a new standard radio signal at 15 MHz starts with an output of 1 kW.
12/1955 (Showa 30)	The prototype passive ammonia frequency standard is completed.
01/01/1956 (Showa 31)	The calibration of the main frequency standard is changed from astronomical timescale UT0 to UT2, still determined by the Tokyo Observatory.
08/1956 (Showa 31)	The GT-cut crystal oscillator type 800 achieves Q = 2.18 million at impedance R = 6 Ω with a sensitivity of 1×10−7 to 1×10−9 per 1°C temperature change.
01/10/1956 (Showa 31)	The Standards Division creates the Crystal Vibration Laboratory and Atomic Vibration Laboratory.
1956 (Showa 31)	Results are shown for a servo-type crystal oscillator with reduced change in oscillation frequency over time. The ammonia standard reaches an accuracy of 1×10−8.
01/1957 (Showa 32)	The first ammonia maser at RRL achieves oscillation, with an accuracy of approximately 3×10−9.
17/06/1957 (Showa 32)	For a radio wave propagation experiment in the International Geophysical Year (IGY), an additional 20 ms long carrier disconnection is included in the time signal. The experiment is repeated in September.
01/07/1957 (Showa 32)	The messages of the IGY world warning network are included in the time signal twice per hour as a Morse code signal at 440 Hz. This is continued until 31/12/1958.
30/09/1957 (Showa 32)	The 8 MHz signal broadcast is interrupted.
30/11/1957 (Showa 32)	The 4 MHz signal broadcast is terminated.
1957 (Showa 32)	A precision frequency comparison device is completed with an accuracy of 3×10−10. Development begins for a new lens-type, AT-cut crystal oscillator unit.
01/02/1958 (Showa 33)	The 8 MHz broadcast resumes as experimental station JG2AE, with 500 W output.
20/08/1958 (Showa 33)	A new transmitter made by Kokusai Denki is put into operation for the standard radio signal.
1958 (Showa 33)	The prototype of a passive ammonia standard, using the power supply modulation method to achieve continuous operation is manufactured by Mitsubishi Electric. A long-term stability of 2×10−9 is demonstrated in the following year. The ammonia 3-3 maser achieves an accuracy of 2×10−9 at the same time.
01/1959 (Showa 34)	Operation starts for a constant temperature bath with a temperature ripple of less than 1/10,000°C, with an internal change of 3/10,000°C per 1°C change in ambient temperature.
16/03/1959 (Showa 34)	The output power of the standard radio signals at 2.5 MHz, 5 MHz, 10 MHz and 15 MHz is increased to 2 kW. Signals are now broadcast 24 hours per day, except for the 2.5 MHz signal that is available only from 16:00 to 8:00. The time is announced every 5 minutes in Japanese and English. A new prototype room 8 m underground is completed.
15/05/1959 (Showa 34)	The experimental long-wave station JG2AQ begins broadcasting at 16.2 kHz, with an output of 100 W.
09/1959 (Showa 34)	The ammonia maser is used for the frequency regulation of the standard radio signal, the first step into the era of atomic frequency standards. It realizes a frequency reproducibility of 2×10−10.
1959 (Showa 34)	The crystal oscillator of type SQ-3 is completed for operation in a double constant-temperature bath. An ammonia maser based on the 3-2 line successfully achieves oscillation.
01/1960 (Showa 35)	The GT-cut crystal oscillator type 900 achieves Q = 3.63 million at impedance R = 10 Ω.
07/1960 (Showa 35)	The 3-2 line, double-beam ammonia maser achieves a frequency stability 1×10−10 and is now used for the frequency regulation of the standard radio signal.
16/08/1960 (Showa 35)	The one-second signal of the 8 MHz JG2AE station is now transmitted by the superposition of a 1.6 kHz signal according to the recommendation of the CCIR.
21/11/1960 (Showa 35)	The output power of the JG2AQ station is increased to 3 kW.
08/1961 (Showa 36)	Two 40 m self-supported steel towers replace the wooden masts for the broadcast of standard radio signals.
01/09/1961 (Showa 36)	The frequency of the standard radio signal, previously based on the UT2 timescale, is changed to be determined by the ammonia 3-2 line, double-beam maser standard. Periodic frequency and time (in steps of 0.1 s) adjustment will ensure agreement with UT2. The frequency offset at this time is −15×10−9. The accuracy of the standard itself is 5×10−9 now. The 1 kHz modulation of the 15 MHz standard radio signal is stopped and only the one-second signal is maintained. Time signals are internationally synchronized to within 1 ms.
10/1961 (Showa 36)	The long-wave phase recorder successfully receives the signal of the NPM 19.8 kHz station in Hawaii. The reception experiment is continued with a separate receiver.
26/12/1961 (Showa 36)	The experimental long-wave station JG2AR begins operation, broadcasting at 20 kHz with 3 kW output.
25/04/1962 (Showa 37)	The Ministerial Ordinance No. 1 amends the duties of the Ministry of Posts and Telecommunications: "The frequency of the standard radio signals broadcast according to the Ministry of Posts and Telecommunications Establishment Law will be monitored by an atomic frequency standard of the Ministry of Posts and Telecommunications Radio Research Laboratory. The deviations from the standard time determined by the Ministry of Posts and Telecommunications will be reported by the Radio Research Laboratory of the Ministry of Posts and Telecommunications."
10/07/1962 (Showa 37)	Two new transmitters for the standard radio signals start operation, produced by Kokusai Denki.
10/1962 (Showa 37)	The Radio Research Laboratory purchases the first commercially available cesium beam frequency standard: The Atomicron.
09/12/1962 (Showa 37)	Test operation starts for a 15 MHz time signal based on the CCIR recommended modulation method. Operation continues until 02/1963.
09/1963 (Showa 38)	The 14th General Assembly of the International Union of Radio Science (URSI) is held in Tokyo. A large number of visitors attend, including Dr Essen, the inventor of the cesium beam frequency standard.
1963 (Showa 38)	Development begins for a compact photoexcitation frequency standard based on a cesium gas cell, which achieves a stability of 1×10−10 in the following year. Work also starts on a hydrogen maser.
01/06/1964 (Showa 39)	The standard radio signals are completely revised to follow the CCIR recommendations. The one-second signal is switched from the carrier interruption method to a 5ms superimposed 1600 Hz signal. Time announcements are now made twice per hour, at 34 minutes and 59 minutes. The frequency now has an accuracy of 5×10−10, the one-second interval 1×10−6, and the time signal is kept within 0.1 s of the standard time. The standard time device is manufactured by Toyo Communication Equipment.
07/1964 (Showa 39)	An precision time synchronization experiment is conducted between Japan and the United States using the Relay 2 satellite.
01/1965 (Showa 40)	The US company Hewlett-Packard (HP) introduces a practical commercially available cesium frequency standard.
15/02/1965 (Showa 40)	A time synchronization experiment is conducted between the Kashima branch of the Radio Research Laboratory and the United Stated Naval Observatory (USNO). Around 02/20, it demonstrates time synchronization to within 0.1 μs. Simultaneously, a collaboration with HP allows the first time comparison between Japan and the United States using a portable cesium beam atomic clock. This provides an accuracy of 1 μs, and the difference between atomic time in Japan and the US is determined to be 1.329 ms.
04/1965 (Showa 40)	Reception experiments begin, using the Loran-C signals broadcast from Iwo Jima for international comparison. Publication of the Standard Frequency and Time Service Bulletin begins.
20/04/1965 (Showa 40)	The Radio Research Laboratory receives the Award of the Minister of Posts and Telecommunications for "Development of the Ammonia 3-2 Line, Double-beam Maser and Related Ultra-Precision Instrumentation" on the anniversary of the Standards Section.
1965 (Showa 40)	Two hydrogen masers are acquired from Nippon Electric Company, Limited (later NEC). Construction begins for a new prototype room.
10/01/1966 (Showa 41)	At 11:00, the experimental long-wave station JG2AS, located at NTT's Kemigawa facility, starts broadcasting at 40 kHz, with 10 kW output power. A rubidium frequency standard is used as the source oscillator, and the frequency accuracy is 2×10−11 for a one-day average.
04/04/1966 (Showa 41)	An AT-cut 1 MHz crystal oscillator with parallel electric field excitation is completed, with Q = 22.39 million.
10/06/1966 (Showa 41)	The GT-cut crystal oscillator type 1000 achieves Q = 5.38 million at impedance R = 17.3 Ω.
06/1966 (Showa 41)	The Radio Research Laboratory is third in the world to achieve oscillation of an active hydrogen maser. A 3-hour comparison with a cesium beam standard shows a stability of 1×10−11.
1966 (Showa 41)	A hydrogen maser replaces the ammonia maser as the main frequency standard. An electronic-bridge crystal oscillator of SQ-4 type achieves a stability of 5×10−11 in the presence of ambient temperature changes up to 10°C. This oscillator will also be used in the standard radio signal generation.
05/1967 (Showa 42)	An NEC 2.5 MHz AT-cut transistor crystal oscillator is installed for the generation of the standard radio signal.
01/06/1967 (Showa 42)	Structural reform of the Radio Research Laboratory: The Atomic Standards Laboratory, Frequency Standards Laboratory and Standard Radio Division are established as part of the new Frequency Standards department. The Crystal Oscillation Laboratory is abolished. The work on crystal oscillators continues within the 4th Special Laboratory until it is ended in 1975.
06/1967 (Showa 42)	Research begins on a rubidium gas cell atomic frequency standard.
10/1967 (Showa 42)	The 13th General Conference on Weights and Measures (CGPM) in Paris defines the SI second as the duration of 9,192,631,770 cycles of the radiation associated with the transition between two hyperfine levels of the ground state of the cesium-133 atom. An international comparison of hydrogen maser frequencies using portable atomic clocks shows that the masers of the Radio Research Laboratory have frequencies near the overall average.
1967 (Showa 43)	A hydrogen maser operating at the hydrogen natural frequency of 1,420,405,751.777 Hz ± 0.009 Hz reaches a stability of 3×10−14, with a reproducibility of 5×10−12.
20/04/1968 (Showa 43)	The Radio Research Laboratory receives the Award of the Minister of Posts and Telecommunications for "Improving the Accuracy of Hydrogen Masers and Frequency Standards" on the anniversary of the Frequency Standards department.
20/05/1968 (Showa 43)	A time comparison experiment is conducted between Japan and the United States, using a portable atomic clock provided by USNO.
10/10/1968 (Showa 43)	Measurements are started in collaboration with the Mizusawa Latitude Observatory, using a portable cesium beam atomic clock to compare frequencies by the long-wave JG2AS signal and time comparisons by the short-wave JJY signal. They find a frequency accuracy of 2×10−11 for a one-day measurement, and a timing accuracy of several μs.
01/1969 (Showa 44)	A time comparison with USNO by using the Loran-C signal of the Iwo Jima station shows a delay of about 40 μs accumulated over one year, indicating a 1.2×10−12 frequency difference. With an accuracy of 0.1 μs, this becomes the main comparison method from this year forward.
1969 (Showa 44)	A Practical Cesium Standards group begins work to replace the crystal standards in the generation of Standard Time.
24/09/1970 (Showa 45)	A very-low frequency (VLF) measurement with multiple closely spaced frequencies (20.000 kHz, 20.080 kHz and 20.081 kHz) is conducted between Koganei and Kokubunji, with an estimated accuracy of 10 μs.
09/1970 (Showa 45)	An international frequency comparison is performed by exchange of the bulb of a hydrogen maser between Japan, the UK and Canada. The measurement matches the Canadian result to within 3×10−13.
12/10/1970 (Showa 45)	Test operation of the JG2AS time signal begins, and uses a cesium standard as reference from 12/10.
12/1970 (Showa 45)	Experiments start to test synchronization between Koganei's cesium atomic clock and atomic clocks in Kemigawa, Kashima, Inu and various Tokyo locations, using the horizontal synchronization of a TV signal. Frequency comparisons are performed using the 3.58 MHz color subcarrier. By 1972, time can be synchronized to 0.2 μs and frequency can be compared with an uncertainty of only 5×10−12 with one hour of measurement.
1970 (Showa 45)	The prototype of a rubidium gas cell standard is completed, with a stability of 1×10−11 for τ = 1 s measurement time.
01/1971 (Showa 46)	Measurements taken throughout Japan over the period of 1967 to 1970 show an accuracy down to few tens of μs for the short-wave signals. The differences between the timing signals of different standard radio signal transmitters are determined and corrected.
08/07/1971 (Showa 46)	JJY begins using a rubidium standard.
01/10/1971 (Showa 46)	Preliminary test of a joint Japan-US time synchronization experiment using VLF.
01/11/1971 (Showa 46)	A special time adjustment delays the standard time reported by JJY by 1 ms.
1972 (Showa 46)	A method is developed that allows operation of crystal oscillators over a wide temperature range without frequency jumps.
01/01/1972 (Showa 47)	The new UTC method is implemented to generate the timescale UTC(RRL). The frequency offset of the standard radio signal is removed, and the time is adjusted by a delay of 0.107620 seconds. The leap second adjustment is introduced to keep the atomic timescale close to the astronomical timescale UT1. The frequency accuracy of UTC(RRL) is 1×10−10.
05/1972 (Showa 47)	RRL and the National Research Laboratory of Metrology begin regular comparison of atomic clocks by TV signal synchronization. The Tokyo Observatory joins the measurements in 04/1973.
01/07/1972 (Showa 47)	The first leap second adjustment is carried out.
1972 (Showa 47)	With the development of cavity auto-tuning, hydrogen masers reach a reproducibility of 1×10−12.
20/05/1974 (Showa 49)	Experimentation building no. 3 is completed at the new location of RRL headquarters in Nukui Kitamachi, Koganei, where NICT's headquarters is still located today.
10/01/1975 (Showa 49)	By improving the magnetic shielding and other details, an improved hydrogen maser stability of 1×10−15 is reported.
10/01/1975 (Showa 50)	The frequency standards facility and research begin their move within Koganei, from Midori-cho to the new RRL experimentation building no. 3 in Nukui Kitamachi.
03/1975 (Showa 50)	The hydrogen maser HⅠ is relocated, and a new hydrogen maser HⅡ is installed.
04/04/1975 (Showa 50)	JJY begins using a cesium standard for its broadcast.
05/1975 (Showa 50)	The frequency deviation of the TV subcarriers of the Japan Broadcasting Corporation (NHK) and Japan Educational Television (NET), transmitted from Tokyo Tower, are now reported regularly, along with the measured emission time of a selected synchronization pulse.
01/06/1975 (Showa 50)	The experimental 8 MHz signal of the JG2AE station becomes the new JJY standard radio signal.
21/06/1975 (Showa 50)	A two-way time transfer experiment is conducted between the Kashima branch and the NASA Rosman tracking station, using the geostationary satellite ATS-1. The experiment uses the Spread Spectrum Random Access (SSRA) method and continues until 28/06, achieving a relative time comparison accuracy of 1 ns. It demonstrate the theoretically predicted Sagnac effect with an accuracy of 10 ns.
11/11/1975 (Showa 50)	An international time comparison experiment is performed for eleven days using dual frequency Omega radio navigation signals and the transmission of the Timation satellite.
12/1975 (Showa 50)	Time comparison experiments are conducted using the unidirectional VHF repeater of the geostationary ATS-1 satellite. The experiments are repeated over ten days until 01/1976.
1975 (Showa 50)	Development starts on the laboratory cesium beam primary frequency standard Cs1. Research on the rubidium gas cell standard is halted.
1976 (Showa 51)	A long-term comparison between USNO and RRL using the data of the NLK station and a portable clock reaches an accuracy of 5×10−14 to 3×10−13 after one year. Seasonal changes of about 10 μs are observed for the propagation path at RRL, and about 1 μs at USNO. Development starts on a stable superconducting cavity oscillator. In the following year, this reaches a frequency stability of 2×10−11 at Q = 107.
01/11/1977 (Showa 52)	The JG2AS station is moved from Kemigawa station to the NTT Nasaki radio transmission station in Sanwa-cho, Sashima-gun in Ibaraki prefecture and begins operating 24 hours per day.
30/11/1977 (Showa 52)	The transmissions of the JG2AQ and J2AR stations end.
01/12/1977 (Showa 52)	The broadcast of JJY is also moved to the Nasaki radio transmission station. Nasaki becomes the first unmanned standard frequency station, connected to the RRL headquarters by a dedicated wired connection, with remote control and remote monitoring. The control equipment is based on integrated circuitry and manufactured by Toshiba (Asia Production Center). The data format has changed completely, with time announcements now made every ten minutes. The power of the 8 MHz signal is increased to 2 kW, and the frequency accuracy is now 1×10−11. The Nasaki system clock is kept within ± 10 μs (with a frequency agreement to ± 5×10−12) relative to the main clock at RRL headquarters by using the TV horizontal synchronization pulses, measured to an accuracy of 0.1 μs and 1×10−12. A practical measurement system is developed.
16/12/1977 (Showa 52)	The Frequency Standards department completes the move to RRL headquarters in Nukui Kitamachi, Koganei.
01/1978 (Showa 53)	Publication of the average atomic time scale TA(RRL) begins, calculated based on the measurements of the Atomic Clock group. This has been in development since 1976.
11/1978 (Showa 53)	A time comparison experiment is performed with USNO over approximately one year, using the unidirectional distance measurement signal of the NTS-1 satellite.
20/06/1979 (Showa 54)	In cooperation with the Radio Control Bureau, time synchronization is established between RRL headquarters, the Mizusawa Latitude Observatory and the Tsushima Omega station for the purpose of radio wave emitter location by arrival time differences.
11/1979 (Showa 54)	A time comparison experiment between Koganei and Mizusawa is performed using the TV synchronization signal and a portable clock. The two methods agree to 0.2 μs, and the accuracy reaches 0.12 μs after about 4 months.
1979 (Showa 54)	Investigations begin on the Majorana effect in hydrogen masers. Development begins for a portable hydrogen maser for very long baseline interferometry (VLBI).
1980 (Showa 55)	Time comparison experiments using the Japanese communication satellite Sakura (CS) begin. Test operation starts for a system to generate atomic time TA in real time.
25/05/1981 (Showa 56)	High-precision time and frequency transfer methods are established from Kashima main station to the MCPC (multiple channels per carrier) station of the CS satellite system.
10/1981 (Showa 56)	An experiment superimposes a time code on a TV signal transmitted by the CS satellite. On reception in Yamakawa, Kagoshima prefecture, a timing accuracy of 5 μs is obtained.
1981 (Showa 56)	The HⅢ hydrogen maser for VLBI is completed. A superconducting cavity oscillator with Q = 1.6×108 is realized. By 1984, it will achieve a frequency stability of 1.4×10−14 after τ = 500 s measurement time. A time synchronization experiment over the telephone network begins. Initially targeting an accuracy of 1 ms, this achieves a synchronization to 0.2 μs in an experiment with Hokkaido University in the following year.
03/1982 (Showa 57)	JJY 8 MHz is registered as a standard frequency station with the International Frequency Registration Board (IFRB).
26/04/1982 (Showa 57)	A two-way time comparison is performed using an experimental device of the CS satellite. It continues until 01/05, and achieves a timing uncertainty of 1 ns and a frequency accuracy of 1×10−13 reached after τ = 100 - 200 minutes of measurement time.
1983 (Showa 58)	Research starts on a photoexcited cesium standard and a trapped ion experiment.
02/1984 (Showa 59)	Operation starts for newly developed time comparison receivers using the L1 band signal (1575.42 MHz) and C/A code of the Global Positioning System (GPS) satellites. This enables Japan's atomic clocks to begin contributing to International Atomic Time (TAI), after they had so far been operated in separation from those in Europe and the United States. The measured data is sent to the International Time Bureau (and to BIPM, the International Bureau of Weights and Measures, starting in 1988). Frequency evaluations by the cesium beam primary frequency standard Cs1(RRL) are also sent occasionally (once or twice per year) to contribute to the calibration of TAI.
10/1984 (Showa 59)	The HⅡ hydrogen maser now operates continuously. Its frequency will be reported to BIH (and later BIPM) starting in 1985. For a time comparison experiment by VLBI, a fringe test is conducted with USNO. This is followed by a baseline length determination in a 24-hour observation in December. The experiment then obtains an accuracy of 0.1 ns.
1984 (Showa 59)	A small spread-spectrum (SS) device is developed dedicated to time transfer by signals of the CS satellite.
14/12/1984 (Showa 59)	The frequency standard calibration service is made available.
08/04/1985 (Showa 60)	As part of a structural reform, the Frequency Standards department is renamed the Standard Measurement department, and the Frequency Standards laboratory is renamed the Frequency and Time Comparison laboratory.
10/1985 (Showa 60)	USNO Richmond station performs a zero-baseline interferometry (ZBI) experiment for in-station delay calibration for accurate VLBI time comparison. An accuracy of 1 ns is obtained.
1985 (Showa 60)	Using the new spread-spectrum device, a bidirectional time comparison between the headquarters and Kashima achieves an accuracy of 2-3 ns. After installing a time comparison receiver for the signals of the meteorological satellite Himawari (GMS), experiments conducted with the Japan Meteorological Agency (Hatoyama) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) of Australia, obtain a precision of approximately 10 ns. The delay of GPS and GMS receivers is measured to an accuracy of 15 ns and 20 ns, respectively.
1986 (Showa 61)	Time comparisons are started with the Australian National Measurement Laboratory (NML) using GMS-3 and GPS signals. GPS comparisons are improved and reach the highest international level with accuracies of 10 ns or better.
01/07/1987 (Showa 62)	The real-time synthetic atomic time (RTA) starts operation as the new generation system for UTC(RRL). It maintains UTC(RRL) within ± 0.1 μs in time and ± 1×10−13 in frequency with respect to TAI.
09/1987 (Showa 62)	A travelling receiver developed at RRL is used to calibrate the delay differences of GMS-3 and GPS receivers used for Japan-Australia time comparison.
1987 (Showa 62)	Satellite Laser Ranging (SLR) equipment is installed at the 1.5 m telescope at JAXA Space Optical Communication Ground Center (SOCG) and experiments with picosecond optical pulses begin.
01/04/1988 (Showa 63)	Measurement equipment, telemetry systems and the recognition signal generator are installed as the first step of a facility renewal for the standard radio signal.
08/04/1988 (Showa 63)	RRL is renamed to the Ministry of Posts and Telecommunications Communications Research Laboratory (CRL).
01/10/1988 (Showa 63)	Renewal of the standard radio signal facility is completed and operation restarted. While keeping the previous concept, the new equipment is automated, downsized, and has enhanced functions. It also supports ROM for time announcements, can superimpose time codes on the long-wave signals, and is adaptable for future changes in transmission format.
11/1988 (Showa 63)	A differential calibration is performed in preparation for time comparison with the Korea National Institute of Standards and Technology (KNRI), using GMS-3 and GPS.
01/12/1988 (Showa 63)	Experimental time code transmission starts on the long-wave signal with one frame per minute.
1988 (Showa 63)	A newly developed GPS dual-frequency receiver enables measuring the total electron content in the ionosphere. It is used in measurements at CRL headquarters and BIPM. The system is also patented and commercialized.
01/1989 (Heisei 1)	Oscillation is achieved in an ultra-compact hydrogen maser, about 1/6 the conventional size.
1989 (Heisei 1)	A same-station return timing experiment is conducted with Intelsat satellites in collaboration with Kokusai Telegraph and Telephone Corporation (KDD). Using the spread spectrum method, it obtains a ranging accuracy of 0.4 ns. The Satellite Laser Range Finder (SLR) at CRL's Space Optical Communications Ground Center (SOGC) successfully acquires laser return signals from the Ajisai, LAGEOS and ETALON laser ranging satellites.
30/01/1990 (Heisei 2)	50th anniversary of the standard radio signal broadcast. A celebration and commemorative lecture will be held on the following day.
1991 (Heisei 3)	Trial operation starts for time distribution by personal computer communication. The telephone time distribution system undergoes maintenance. A two-way time comparisons experiment is conducted between CRL headquarters and the Kashima facility.
21/06/1991 (Heisei 3)	The superposition of time code on the long-wave signal is extended to all days.
1992 (Heisei 4)	A stability of σy(τ) = 1×10−5/τ is found for observations of the millisecond pulsar (PRS-1937+214). The accuracy of the cesium primary frequency standard Cs1 is evaluated as (0.26 ± 1.08)×10−13. Two-way time comparisons are conducted with the Korean Research Institute of Standards and Science (KRISS) and the Taiwan Telecommunications Laboratories (TL) using the Intelsat satellite. Development begins for time synchronization by network.
1993 (Heisei 5)	The Cs primary standard Cs1 obtains a stability of 2-3×10−14 with 10-20 days of averaging time.
01/1994 (Heisei 6)	Measured ionospheric delay data is now reported to BIPM for use in GPS time comparisons.
1995 (Heisei 7)	Cesium atoms in a gas cell are successfully trapped and cooled.
01/04/1995 (Heisei 7)	The data previously reported in printed form is now available on the Horonet/BBS electronic bulletin board system. The print publication is ended.
01/08/1995 (Heisei 7)	Operation of the Telephone JJY system starts.
31/08/1995 (Heisei 7)	Joint research begins with Internet Initiative Japan, Inc. for standard time distribution via the Internet.
03/1996 (Heisei 8)	The operation of the JJY 2.5 MHz and 15 MHz stations is stopped, and only three frequencies are transmitted now.
09/1996 (Heisei 8)	Electronic data publication by WWW begins.
1997 (Heisei 9)	Joint research with Anritsu Co., Ltd. starts on an atomic frequency standard for spacecraft. A two-way time comparison is performed between Japan and Australia (NML) using the Intelsat satellite.
1998 (Heisei 10)	The new optically pumped cesium primary frequency standard CRL-O1 is evaluated to an accuracy of 2×10−14. A time comparison experiment using a 2.4 Gbps optical link is performed between the CRL headquarters and the Yokosuka branch. It is compared to the results of a two-way satellite comparison. Experimental comparisons between the timescales of Japan and China (CSAO) begin by two-way satellite transfer.
31/03/1998 (Heisei 10)	The Horonet/BBS system is shut down, all public announcements are now available via WWW.
04/1998 (Heisei 10)	CRL now offers a calibration service for equipment needed for radio station certification inspection.
1999 (Heisei 11)	Two-way satellite comparisons are performed with the National Research Laboratory of Metrology. Special measures are implemented to avoid Y2K problems.
09/06/1999 (Heisei 11)	The Naganami experimental station JG2AS stops operation.
10/06/1999 (Heisei 11)	The official operation of the long-wave standard radio signal begins. The JJY 40 kHz signal is transmitted from the Otakadoya-yama radio transmission station.
12/04/2000 (Heisei 12)	CRL receives the Award of the Minister of Posts and Telecommunications for the development of the long-wave standard radio signal facilities.
06/01/2001 (Heisei 13)	As part of a reorganization, the Communications Research Laboratory becomes part of the Ministry of Internal Affairs and Communications (MIC).
19/03/2001 (Heisei 13)	A ceremony at Nasaki transmission station commemorates the end of the short-wave standard radio signal broadcasts.
31/03/2001 (Heisei 13)	All short-wave standard radio signal transmissions are terminated. Only long-wave signals are available from now on. The frequency calibration service is certified to conform with ISO/IEC 17025 by the Product Evaluation Center of the Ministry of Economy, Trade and Industry (13th Review, No. 341).
01/04/2001 (Heisei 13)	The Communications Research Laboratory is incorporated as an independent administrative agency.
01/10/2001 (Heisei 13)	The opening ceremony of the Hagane-yama standard radio signal transmission station is held in Fukuoka city. The broadcast of the JJY 60 kHz signal begins.
24/10/2001 (Heisei 13)	A Japan Standard Time display is installed in the lobby of the Ministry of Internal Affairs and Communications, it is introduced by Minister Katayama. The long-wave standard radio symposium is held in Tokyo.
2001 (Heisei 13)	The Electronic Time Authentication project is started.
31/01/2003 (Heisei 15)	CRL receives ASNITE-NMI certification for time and frequency measurement.
01/04/2003 (Heisei 15)	CRL is declared a designated calibration organization by the Ministry of Economy, Trade and Industry.
01/04/2004 (Heisei 16)	The National Institute of Information and Communications Technology (NICT) is created as an incorporated administrative agency by merging CRL and the Telecommunications Advancement Organization (TAO).
10/06/2004 (Heisei 16)	A commemorative card is issued for the 5th anniversary of the long-wave standard radio signal broadcast.
28/12/2004 (Heisei 16)	The regular report of the TV color subcarrier frequency deviation is ended.
21/01/2005 (Heisei 17)	The Time Information service is introduced.
01/02/2005 (Heisei 17)	The Time Business service is introduced.
08/02/2005 (Heisei 17)	Full scale operation starts for the distribution of Japan Standard Time by NTP, the Network Time Protocol.
27/05/2005 (Heisei 17)	The Remote Frequency Calibration service is introduced.
22/07/2005 (Heisei 17)	A two-way satellite time comparison link is established with the German Federal Physical-Technical Institute (PTB).
21/12/2005 (Heisei 17)	The Hagane-yama standard radio transmission station is damaged by a lightning strike.
01/2006 (Heisei 18)	The timestamping platform is experimentally demonstrated.
07/02/2006 (Heisei 18)	The Japan Standard Time system is updated, making it five times more accurate.
12/06/2006 (Heisei 18)	Japan Standard Time is now distributed by the world's highest performance NTP server. A public contest is held for development of NTP client software, and winners are announced on 15/12/2006.
01/07/2006 (Heisei 18)	Work begins on an optical lattice clock frequency standard.
26/01/2007 (Heisei 19)	The remote calibration service is accredited within the Japan Calibration Service System (jcss).
01/04/2007 (Heisei 19)	The capability of the bring-in frequency calibration service is improved from 1×10−13 to 5×10−14.
05/2007 (Heisei 19)	International measurements survey the electric field strength of the long-wave standard radio signals.
04/2008 (Heisei 20)	The cesium fountain clock CsF1 is internationally recognized as a primary frequency standard, with a systematic uncertainty of 2×10−15.
2008	The absolute frequency of a calcium single-ion (Ca+) optical clock is determined for the first time in the world, with an accuracy of 1×10−14. The result contributes to the recommended frequency determined by the International Committee for Weights and Measures.
06/2009 (Heisei 21)	10th anniversary of the Otakadoya-yama standard radio transmission station. Commemorative cards are issued.
01/2010 (Heisei 22)	The uncertainty of CsF1 is reduced to 1.4×10−15.
02/2010 (Heisei 22)	Additional NICT NTP service is started at the facilities of the Japan Internet Exchange (JPIX) to reduce network latency.
03/2010 (Heisei 22)	A trusted time source for electronic time authentication is implemented according to ITU-R SG7 TF.1876.
03/2011 (Heisei 23)	The Otakadoya-yama standard radio transmission station is stopped due to the Fukushima Dai-ichi nuclear power plant accident. The transmitter is modified to support remote operation and resumes broadcast in 08/2011.
05/2011 (Heisei 23)	The time distribution and auditing method for electronic time authentication is standardized according to JIS X 5094.
09/2011 (Heisei 23)	The ASNITE certification is updated to include capabilities for time calibration and an extended frequency range.
10/2011 (Heisei 23)	10th anniversary of the Hagane-yama standard radio transmission station. Commemorative cards are issued again.
11/2011 (Heisei 23)	The TCTF Technical Workshop on Guidelines for CMC of the Asia-Pacific Metrology Programme (APMP) is held at NICT.
2011 (Heisei 23)	Strontium optical lattice clocks at the University of Tokyo and NICT are compared by an optical fiber link. Agreement is demonstrated with an accuracy of 7×10−16.
01/2012 (Heisei 24)	The Sr optical lattice clock achieves an accuracy of 5×10−16, and its frequency is determined with an uncertainty of 3.3×10−15. The results contributes to the work of the International Committee for Weights and Measures, which recommends frequency values for atomic clock transitions in terms of the definition of the SI second.
07/02/2013 (Heisei 25)	The NICT Workshop on the Optical Frequency Standards is held at the headquarters in Koganei. Researchers representing various countries discuss the status and future development of single-ion optical clocks and optical lattice clocks.
2013 (Heisei 25)	A facility for decentralized generation of Japan Standard Time is established at NICT's Future ICT Research institute in Kobe. Research starts on management of a decentralized timescale. Strontium optical lattice clocks at NICT and PTB in Germany are compared by carrier-phase two-way satellite time transfer. Frequency agreement to 1.6×10−15 is demonstrated.
05/2014 (Heisei 26)	Work starts on a renewal of the Hagane-yama standard radio transmission station. It will be completed in 01/2016.
10/2014 (Heisei 26)	Work starts on a renewal of the Otakadoya-yama standard radio transmission station. It will be completed in 03/2016.
04/2015 (Heisei 27)	The time distribution and auditing methods for electronic time authentication are standardized according to ISO/IEC 18014-4.
05/2016 (Heisei 28)	Generation of the world's first real-time generated time signal based on an optical clock begins. The experiment continues for five months.
05/2016	Experimental operation of standard time supply over optical telephone line begins.
05/2017 (Heisei 29)	The absolute frequency of an indium single-ion (In+) optical clock is determined with an accuracy of 5×10−15.
06/2018 (Heisei 30)	As part of the decentralization project, generation of Japan Standard Time at the Kobe sub-station begins.
10/2018	Start of a measurement campaign to compare optical lattice clocks at NICT and the Italian National Institute of Metrology (INRIM) using VLBI techniques developed at NICT, with the support of the Italian National Institute of Astrophysics (INAF). The results with an accuracy of 2.8×10−16 are reported in 2020/10.
11/2018	The International Bureau of Weights and Measures (BIPM) recognizes NICT's optical lattice clock NICT-Sr1 as a secondary frequency standard. It begins contributing calibration reports for International Atomic Time in 12/2018.
02/2019 (Heisei 31)	The Hikari Telephone JJY service begins official operation.
06/2019 (Reiwa 1)	20th anniversary of the Otakadoya-yama standard radio transmission station.
08/2021 (Reiwa 3)	The generation of Japan Standard Time now includes measurements by the optical lattice clock NICT-Sr1 when available.