Matt has got it all down. I have one too but I just let it run continuously when printing so I know when to move prints. I have used it for enlarging in the past, but for precise work you would want a digital enlarger timer that allows for fractions of a second. You also want to set it to focus or off when setting the time, as you can potentially damage the gears inside if you turn back the hands when it is running forward. When you get it, make sure it zeros out correctly, with both minute and second hands coming to a rest at 12. If they are not you have to adjust it, very easy to do, an Allen key/hex wrench under the second hand, and a Philips head under the minute. (atleast those are the types on mine)