Doug, In addition to the comments by Bill (re. the degrading of civilian GPS signals by DOD at various times), I would add that you should be certain that your GPS is using the same Datum as your chart. There is a notation on the chart stating the Datum (i.e.. NAD 83 or WGS 84). There is also a list of Datums to select from in your GPS (in my Garmin 48 it's on the Navigation Setup page). If the Datums don't match you won't be able to translate your GPS position to your chart or vice versa. I believe it is most likely the workings of the Dept. of Defense. I have seen them turn off some satellites completely from time to time which is extremely frustrating when you are using GPS for survey work!!! Don't ever bet your life that the GPS is right, always verify your position by some other method if possible. If you are unable to verify then sail with increased caution. "This new ship here is fitted according to the reported increase of knowledge among mankind. Namely, she is cumbered end to end, with bells and trumpets and clock and wires, ... she can call voices out of the air of the waters to con the ship while her crew sleep. But sleep Thou lightly. It has not yet been told to me that the Sea has ceased to be the Sea." -- Rudyard Kipling Fair Winds Mark Dvorscak M17 #400 GRACE