Hi Jeremy -- I actually think the GPS itself was OK, if you think of it in terms of lat/long data delivered off satellites. The displayed lat/long of the boat was correct. The displayed lat/long of the cursor was correct -- although the bearings to it were not, which I assume come from some internal system calculations.

Even the traditional compass seemed to be correct -- when we thought to check it.

I guess I'm wondering if some momentary effect from the anomaly (I don't really understand how that effect works -- for how long, or how it's manifested) could have confused the system so that its internal calculations got messed up. And stayed messed up.

Your mention of LORAN reminds me of the incident shortly after we bought the boat 18 or so years ago, before we did any upgrades. I didn't know anything about LORAN and just used the display at the nav station to record the given lat/long positions. One afternoon, as I was dutifully recording our position in the log, I realized something was wrong. We were sailing in New England, but it gave our position as somewhere in North Dakota.

First thing we did was upgrade the electronics.