The basics: Film and Paper settings shift time to 68F, hotter=faster, film is dimmer than paper, stick the temp unit in the developer and the other plug is for a switch, I've used the supplied footswitch until it broke. I now use a simple on/off switch. I keep thinking mine is done for but after fiddling and a bit of repair, mine keeps going. I just wish that the temp sensor wasn't fully embedded in plastic resin, that phone cord is starting to get some wear after 25 years and should be replaced. The instructions give an account about the components used in the unit, of which I am begrudgingly impressed with, in my book they've stood up well over time. I'm not too sure that it would be possible (these days) to make another unit of quality, surely cheaper but not in durablity.