SDs for distoX surveys

[Wookey]

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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