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? Graham -----Original Message----- From: Survex <survex-bounces@survex.com> On Behalf Of Wookey Sent: 04 August 2018 01:37 To: Survex User Group <survex@survex.com>; Therion List <therion@speleo.sk> Subject: SDs for distoX surveys Has anyone thought about what the correct SDs for distoX/distoX2 (as opposed to compass and tape) surveys are? I reckon distoX surveys have significantly lower expected error, due to the 'measure 3 times' leg feature (if used) and just higher accuracy due to instrument itself, ease of taking readings (no need to get head near station), and no difficulties with steep legs > 15 degrees. Seems to me this means that we should be using different SDs for these surveys (at least for bearing and inclination readings - length is not obviously more reliable), but I'm not sure how to quantify those improvements. Anyone got any ideas what numbers to use? Wookey -- Principal hats: Linaro, Debian, Wookware, ARM http://wookware.org/