Time Service provides USNO Master Clock time via dialin modem on line

(202) 762-1594 = DSN 762-1594

The communications parameters are:

The format of data is:
MJD DOY HHMMSS UTC cr/lf
* cr/lf
The "*" is the on-time mark for the preceding time information, and is delayed by .0017 seconds (+/- .0004 sec.) from UTC(USNO).

The timing generator which produces this data stream is driven directly by the Master Clock's reference signals without computer intervention.

The modems on line are compatible with Bell 212A and CCITT V.22 standards. They also support CCITT V.54 Remote Digital Loopback (RDLB). The Hayes command for RDLB is AT&T6. After the RDLB command is sent, any characters sent will be returned to the sender. Count the time it takes for a character to return, divided by two, and you will have the time delay between the two locations. This correction can be added to the time mark for high accuracy synchronization.

The Julian Day (JD) is a continuous day count from 4712 BC. The Modified Julian Day is the Julian Day minus 2400000.5.


For links to software for setting time on computers, see
Time Synchronization Software and Gordon T. Uber's comprehensive listing.

Some available programs using the USNO modem service for setting time in PCs include:

  • nisttime, by John J. Rushford (wjjr@alisa.org), available as a gzipped tar archive via anonymous ftp to sunsite.unc.edu. The current release supports SunOS, Linux, and Unixware SVR4.2.
  • Professional TIMESET
    Life Sciences Software, (206)387-9788
  • RightTime Air System Technologies, Inc.
  • Call Time
    Anderson Consultant, (518)477-4934
  • Set Clock for Macintosh
    Jim Leitch, (416)496-0828 , 70416.1532@CompuServe.com
  • Atomic Clock
    Parsons Technology 1-800-223-6925
  • More sources compiled by Marcus Williamson for Compuserve.
  • Time program ftp site

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