Two Identical GPS Units -- Different Accuracies? in GPS technology and devices Posted January 5, 2010 The only established (out here in the Real World) way of accurately determining how accurate a particular GPS unit is, is to compare that unit's coordinates for a specific Benchmark (Only Benchmarks with with OFFICIALLY ESTABLISHED and ADJUSTED coordinates qualify) , and then only with repeated visits over multiple days.I agree with repeated visits to a fixed, known location over multiple days. But how is "an established benchmark with officially established/adjusted coordinates" better than any other fixed, known locaction? The only advantage I see with an "established" benchmark is that I know what my GPS should read before I get there the first time. But after that? My mailbox isn't a moving target. If a GPS will routinely give the same coords for that spot (within a couple of metres), I think that's a good enough test. Come on Lee, surely with your experience you are smarter than that. If your GPS repeated EXACTLY at your mail box 237 times in a row, that proves ABSOLUTELY NOTHING about accuracy. It would only prove that your unit is consistent with itself. Consistently wrong is just as probable as consistently right. Only when you compare your "consumer grade GPS" coordinates to official Benchmark coordinates ("adjusted") which were established to accuracy tolerances that consumer grade equipment is incapable of achiving, can you start determining the accuracy of your unit. Also, only checking once, proves nothing. Why? Because "one in a row" does not make a pattern.