Hi, I have nearly completed the total survey for the system I am mapping. In total, there are a series of little caves (actually mines, but I will stick with the word "caves" because it is clearer), a blind surface shaft, and a couple of significantly long caves. In total, these were surveyed over a series of 6 trips. On one of those trips, we surveyed the surface, and any short fragments of passage that we encountered that way. One of those fragments turned out to be one of the major caves. The major cave's survey was subsequently completed on another trip, but its first few metres are included in the surface survey. I am used to Survex. Each of the surveying trips has its own .th file: overall.th ("input"s all the other files) surface1/surface1.th (contains the entrances to several fragments, and the first 2 legs of cave 1) surface2/surface2.th (contains the blind shaft's plumbed depth and some other entrances) cave1/cave1.th (does not contain any entrances, but is a long cave, connected to the "cave 1 legs" in surface1.th cave2/cave2.th (contains the first part of cave2, and its entrance) cave3/cave3.th (contains cave3, with two entrances) cave2ext/cave2ext.th (contains the second part of cave2) Cave1 is connected to cave2. Each entrance is marked using "station 2 Cave1 entrance" in the centreline section of the file where it is defined. Survex only displays aggregate statistics. Therion tries to identify "caves", which is a concept I am not used to. I had hoped that Therion would be smart enough to see that caves are connected to each other, and work out the connected lengths. But it seems that it only works out the length of the files within the same survey. Cave1 doesn't get any length. Cave2 gets only the length from cave2.th - the length of the cave2ext and cave1 are not included. How do I make Therion realise what caves are connected? Do I need to put them into a structure like this? survey overall survey cave1_2 -entrance 2@cave2 -name "Caves 1 and 2" input cave1.th input cave2.th input cave2ext.th endsurvey endsurvey And if so ... how do I tell it that *part* of the cave lies within the surface survey file? Do I need to split the surface survey up into parts, one of which is the entrance to cave1? Separately, when using "statistics topo-length on", it ignores the surface survey legs, which is quite unfair for the person who surveyed 1 km of surface to link all of the entrances - they get no credit at all. Can it be asked to include surface legs in the topo-length calculations for survey credits? Thanks for any advice. Tarquin