On 2018-08-05 08:44 +0200, Graham Mullan wrote: > I am not sufficiently versed in the maths to suggest what figures might be > used, but I do want to know why you think that the 3-times feature might > affect the expected error for the angles but not for the length?
The 3-times thing greatly reduces blunders. Blunders are usually in compass and clino readings, rather than length readings. But you are right that the 3-times measurement improves all 3 readings (I assume that's what you were implying). Now the SD doesn't represent blunder frequency as it's really about expected mesurement error, but in practice we use it for blunder distribution too, so that's why a lower SD for surveys done this way makes sense to me. If we put in all three versions of the leg then we could leave the SDs the same, but that's not often done (depending how you get your data out of a distoX). Similar considerations apply to backsighted surveys, where both sets of readings _are_ normally entered. Wookey -- Principal hats: Linaro, Debian, Wookware, ARM http://wookware.org/
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