One of the earlier electronic timers (Beseler?) had a metronome built in. I have always used one for burning and dodging - often I need 2 or 3 times the base exposure, or I want to dodge an area for part of the timed exposure. I don't know how to dodge places any other way unless you want to make a whole bunch of timed exposures. Just start your timer for, say, a 20 second exposure, and with your metronome you can dodge 5 seconds here, 3 seconds there etc. It is much the easiest way to print.