I have a sneaking suspicion that offset 1 is not a 'sort' order. (Namely because HWP ammo has this number very very high) I'm thinking that its an index. I believe I found the offset for the space an items takes in GEOSCAPE.EXE at 0x5db34. Each item gets 1 byte which is the space it takes up (10x what is shown on the table at General Stores#Nuts and Bolts, thus I'm hypothesizing that stores have 500 space for items. I'm double checking some things, but I think offset 1 is an index to this array. I'll have details later --Pi Masta 14:39, 5 March 2007 (PST)
Well I indexed the 'sort' number from each of the items to the offset I found. Everything lined up with the space needed for the item (for those applicable) except the Fusion Ball Launchers and Plasma Beam. Their sizes were swapped. At first I thought that my guess of it indexing to this was wrong, but I wanted to double check. Turns out that this page has them backwards. Essentially the sell prices helped me verify which item this file was talking about. I'll make the appropriate changes, and probably put a more indepth explanation on my talk page. --Pi Masta 15:16, 5 March 2007 (PST)
To make modifications to PURCHASE.DAT take effect, you need to replace a PURCHASE.DAT file in a saved game with your edited version, then load the saved game. Changes to PURCHASE.DAT in MISSDAT have little or no effect (except perhaps if you recovered from a crash).
It seems likely that PURCHASE.DAT is copied from a File Template in the GEOSCAPE executable, into the saved game folders and MISSDAT.
This is probably generally true for editing most or all of the GEOSCAPE save files.
Spike 20:19, 7 March 2010 (EST)