I have a small GPS device (Dual XGPS), and today I used it to measure the coordinates of my observing site. Then I went to Xavier's interactive eclipse map and click at the location on the map. The interactive map would show the coordinates as well.
The issue is, the coordinates do not match. The longitude shown by the GPS device (on its iPhone APP) is a whole 1' west to the coordinate shown on Xavier's interactive map. 1' is a whole lot. Something like several hundreds times larger than the possible error of my click on the map. It can lead to 1 to 2 seconds of time difference for C2 to C3 in SEM.
So, I wonder which one I should trust. The hardware GPS? Or the map?
It's also a bit strange that the offset is exactly 1'. Not 1'15", not 56", not 1'06". It's 1'00". If it's someone's handwriting, I would say it's a typo of a single digit among those many digits. But it's not handwriting.