Dwight> Hi I thought I'd mention that GPS satellites are very precise Dwight> but no longer accurate. The world standards like UTC are not Dwight> on the same second as used for GPS. I don't recall how far Dwight> things have changed but for political and other reasons, the Dwight> world time standards have been changing. GPS are still locked Dwight> to being relative to particular data and time. Every one else Dwight> has had a few leap seconds here and there. There is a chart Dwight> someplace on the web that shows how things are. The fact that GPS time doesn't have leap seconds and UTC does, doesn't make GPS time inaccurate. It just means there's a known adjustment between the two, no different from what you do when you allow for timezones. I didn't realize that GPS time omits the leap seconds, but that makes perfect sense -- if you tried to include them, it would just add a completely unnecessary complication to the system. By the way, leap seconds are NOT political. They are made (by the BIH, International Time Bureau) when UCT -- which is basically time reckoned by cesium clocks -- has drifted more than about 600 ms from time as set by the earth's rotation. Since the rotation time of the earth is not constant, that difference is subject to change, somewhat unpredictably. So leap seconds are inserted on an "as needed" basis. paul