In January, 1995, a time and frequency distribution system was put into operation. A "Site 1Hz" tick is generated by a TRAK master clock from a 5 MHz signal from the Sigma Tau hydrogen maser standard. The tick and also an IRIG time signal is distributed around the Green Bank site on fiber optics. A clock offset measurement system logs offsets between various clocks about every 10 minutes. Files listing these offsets are placed in the anonymous ftp area on osiris under directory "timer". March 20, 1995 - adjust Site1Hz to be close to GPS. ST-GPS ~ -50ns. July 26, 1995 - adjust SAO offset by 10us. Old ST-SAO (at 140ft) = -9.4us New = +0.5us. Dec 6-7, 1995 - Change Sigma Tau maser rate by 1 in 10**8 for GBTIE2 run. offset ST-GPS drifted to -922us over 24 hours. Rate put back to normal, with slight rate change to better match GPS, at 21:42UT on Dec.7th. ST 1pps offset adjusted to about 0.2us. Dec 15, 1995 - re-create all 1995_MM.tdat files to include the right SAO correction. The (ST-SAO) and (GPS-SAO) values measured at the interferometer, now have 5766 ns subtracted, to correct for the cable delay between the 140-ft building and the interferometer building. Jan 19-22, 1996 - Power outage. 1PPS tick offset re-set. Recording of timing data off line. Jan31-Feb.1, 1996 - Site 1pps from TRAK reset because power to TRAK master clock accidentially cut off. Feb.27, 1996 - reset Site1PPS (TRAK) April 11, 1996 - added new input "TAC" to time logs. This is a GPS receiver from T.A.Clark. May 17, 1996 - Adjust TRAK 1pps offset. TRAK had lost time due to power glitch. May 22, 1996 17:19UT - Change ST maser rate by 10**-8 for GBTIES3 run. April 15, 1997 - 1PPS fiber distribution system removed, modified for receipt of 1pps from the SAO maser by fiber, and re-installed. This should not have affected the Site Time 1 pps, but seems to have caused a 2 us offset. Previously, SAO 1pps came to the timing center on coax, with delay=5766ns. Now the SAO 1pps comes on fiber, with delay=12581ns. April 18, 1997 - Replaced 5 MHz cable from maser to 5MHz distribution amp and replaced cable from 5MHz distribution amp to TRAK master clock. Reset Site 1 pps to near GPS. May 2, 1997 - Power supply in timing rack replaced. Reset Site 1pps. About 100 ns change in site 1pps. July 1997 - Add *.ttac files, giving offsets to GPS as measured by the "TAC" GPS receiver, more accurate that the old DATUM GPS receiver. Also note the DATUM GPS is not working properly in July and August -- it gives about a 1 ms offset to the maser. Sept 1997 -- DATUM GPS has been reset and now gives a correct 1 pps. Nov 21 1997 -- TRAK clock lost power while testing the UPS system. Site 1pps reset. Oct 29, 1998 -- Sigma Tau maser and timing rack moved to new location in the Reber lab GBT equipment room. New timing measurement matrix: X0 = Site 1 pps X1 = TAC GPS X2 = 140ft maser (cable delay is now 9231 ns on fiber) Y0 = VLB20_1 (VLBA formatter for 20-meter) Y1 = VLB20_2 (backup 20-m formatter) The only GPS in use now is the TAC. The files in the /o/ftp/timer directory for each month are: yyyy_mm.t0 (offsets referenced to Site 1 pps) yyyy_mm_ttac (offsets referenced to TAC; SAO corrected to 140ft). Oct 30, 1999 -- SAO maser moved to Reber Lab GBT equipment room. SAO maser cable delay is now zero.