This is a Survex issue but may also be of interest to this list. Plus the Survex list does not accept my 7 KB of data as it says my post is too big. Posting the data here for lack of a capable list for Survex. Footleg ---------- Forwarded message ---------- From: "Footleg" <drfootleg@gmail.com> Date: 17 Jun 2013 14:38 Subject: Diving data loop closures altering depths To: "survex" <survex@survex.com> Cc: Trying to track down why some underwater data was several metres higher than a sump water surface, I discovered that closing loops between stations at the same depth in diving data alters the depth of surrounding data. This was not expected! I've attached a fragment of the data which illustrates this. Without the loop closed: Station entrance.030 is at depth -5.30 Closing the loop: *equate Entrance.010 EntranceLoopNorth.019 where both these stations are at the same depth, but horizontally displaced (a common scenario as depths are absolute but length and compass errors accumulate in diving data), now: Station entrance.030 is at depth -5.48 Is this a bug, or have I not understood something here? Footleg