In my own experience, the most common blunder which the 'measure 3 times' method with DistoX2 catches is mis-read distance. The Disto tends to be used in the same orientation for all 3 shots, so the compass and clino tend to be well aligned in all 3 (regardless of how well calibrated the DistoX is, or is there are local magnetic fields throwing the compass). But the laser does sometimes miss the target and overshoot, resulting in one of the 3 shots being out of tolerance for PocketTopo to count them as a valid leg. Of course catching blunders so they never make it into the data (we would reshoot when it happens) is not the same as the SD in the measured data.
The way we catch bad calibration problems or local magnetic interference is to take backshots (3 of them). This has saved serious errors on multiple occasions which would not have been detected taking shots in one direction alone. Footleg
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