i put together comments to all the posts about "extend" (1) yes, -1 = left, 1 = right and vert is in the middle (0) (2) evaristo, with his proposal of idealized profile not only suggested a way to control shortening, but that also allows stretching. that's good (3) bruce described a procedure for a program to automatically decide how to draw splays in the extended profile. it's more or less what topodroid implements: at a station the range of azimuths is divided into angular sectors one for each leg at that station. a splay is "projected" using the leg of the sector its azimuth falls in. (by the way, to really be in bad luck one need three vert in a row) (4) a program may assign extends to splays automatically, but the user should always be allowed to override what the program does. (that's why a user can set extend also for splays, in topodroid) (5) "cave length": in the (old) manuals i studied that the cave length is "computed" measuring the length of an ideal line that goes thru the middle of the passage. now it is rather cumbersome to compute that line, and all the programs uses the length of the midline, with some discount (duplicate in therion, L in compass, and so on). the problem, i think, is that cave length is not a thing that can be well-defined. so the numbers we give for cave length are an approximation of a fuzzy concept. marco