A known model, or a new one
If the model is on file, its parts and fitments come up with it, and disassembly is guided by what you recorded last time. If it's new, you build the record as you tear it down — and it's waiting for the next one.
The first time you break a unit down it's new; the tenth time, the catalog already knows every part and what it fits. Recognition compounds — the more you've cataloged, the less you ever look up.
See how fitment is built both ways