GPS Week Number Rollover
The GPS Week Number count began at approximately midnight on the evening
of 05 January 1980 / morning of 06 January 1980. Since that time, the count has
been incremented by 1 each week, and broadcast as part of the GPS message. The
GPS Week Number field is modulo 1024. This means that at the completion
of week 1023, the GPS week number rolled over to 0 on midnight GPS Time of the
evening of 21 August 1999 / morning of 22 August 1999. Note that this corresponded
to 23:59:47 UTC on 21 August 1999.
|Week beginning |
at 0000 GPS Time on
|GPS Week Number
|08 Aug 1999||1022|
|15 Aug 1999||1023|
|22 Aug 1999||0|
|29 Aug 1999||1|
It is the responsibility of the user (i.e., user equipment or software)
to account for the previous 1024 weeks.
Depending upon the manufacturer of your GPS receiver, you may or may not have
been effected by the GPS Week Number Rollover on 22 August 1999. Some
receivers may display inaccurate date information, some may also calculate
incorrect navigation solutions.
Contact the manufacturer of your GPS receiver if you have been effected by
the GPS week number rollover. Contacts for some GPS receiver manufacturers
can be found at
GPS World's Buyers Guide.
For more information, please refer to the following websites:
US Naval Observatory Home Page
What Time Is It? USNO Time Service Home Page
GPS Home Page at USNO