| I have a Surveyor's plot map from about 1963. It is no more than about 2k feet on a side. I have tried to calibrate it with five known GPS points from a survey on it's North side that has two small bends in it, otherwise it is pretty much a straight line. Despite my efforts, the calibration comes out way off and to my surprise, it even gets North wrong. If I could overlay a Google satellite map on it, I could work out a few more points.