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.