I have download an old 1923 USGS 15 minute map of Buda IL quadrangle. As far as I can tell, the coordinates on the map are wrong. If I hand measure the coordinates on the map using a map scale ruler graduated in seconds, that measurement comes out to be pretty much the same as the coordingate given by TerraGo. If I check the coordinates on newer USGS maps or Google maps, there is a slight difference. The TerraGo coordinates give a number that is about 0.40 seconds to far to the north, and 1.39 seconds that is to far to the west. That makes a difference of around 100 feet. I would like to get better accuracy than that. I have messed around with the Set Projection Perameters - Custom window. I have entered various numbers into the Origin, Maridian, False slots, and into the Tranlation and Rotation slots, but they haven't changed the reading of the coordinates shown by TerraGo.
Is there a way to adjust the TerraGo settings to compensate for the error so that the coordinate shown by Terrago are more accurate to the true coordinates?
Thanks,
Harry