Hello again, I've done some more experimenting with extended elevations and have discovered some things that may be useful to other people and some bugs (or maybe features I fail to understand!). All the files I refer to below can by found on my ftp site: ftp://ftp.gns.cri.nz/incoming/JennyB/therion/ along with the dataset (107.3d) (1) therion and survex can extend the same data differently. I don't think this is a bug in either software, they just use a different methodology. If you start off by using survex's extend command to generate a extended 3d file to read in to therion and later switch to reading in your un-extended 3d file directly into therion you risk getting very confused, and having to break different loops. See: survex_extend.png shows 107_extend.3d, generated by running "extend 107.3d 107_extend.3d" therion_extend.pdf is when I used: "import 107.3d -surveys use" in therion (2) therion can behave unexpectedly if the data has been extended already in survex, I suspect this is due to the fact that some stations now exist in two different locations after loops have been broken. therion_107_extend_3d.pdf used: "import 107_extend.3d -surveys use" in therion, having first run "extend 107.3d 107_extend.3d", I had expected it to look the same as survex_extend.png Due to this, I decided to extend the data in therion not survex for now at least (I've no idea if this is the correct approach or not!). So, I read in a not-extended .3d file (107.3d), the same file I would use to make a plan survey in therion. I've then discovered a few more things... (3) choosing the correct station name is critical. Some stations legitimately have two different names i.e. the final station on one days survey may also be the first station on the following trip. In this case, ropefree.18 is the same as envelope.1, these are marked in survex with: *equate ropefree.18 envelope.1 When it comes to drawing up the plan I believe you can use either station name. This isn't always the case for extended elevations, often only one works, and the other really doesn't giving huge distortions. I don't know why this happens, as they are not always at junctions or involved in loops. I assume this is a bug? In this example, if I use envelope.3 it looks rubbish (envelope_3.pdf) but if I use ropefree.18 (ropefree_18.pdf) it looks fine (the only difference in these two outputs in the station name, I have several example of this for this dataset). (4) the order matters: "extend ignore china.29 china.27" does what I would expect, but "extend ignore china.27 china.29" does nothing, but gives no error. Look at the bottom right on: china_27_29.pdf china_29_27.pdf this seems wrong to me, and caused me quite a lot of confusion. Sorry if my email has got a bit long and unclear, hopefully it makes some kind of sense! Does anyone else have any helpful thoughts on successfully generating extended elevations? Am I missing some obvious things? Are some of my conclusions above wrong, or are there neat ways around them? Thanks, Jenny