With the negative in place and the image composed on the easel and focused, you will take an educated guess as to the correct f/stop for your enlarging lens. Ideally an exposure will be in the 20 to 40 second range. Now with the lights off and the f/stop set and desired contrast filter in place you are ready to make a test. I make tests that are from 5 seconds to 42 seconds in about 1/3 stop increments. That is 5 seconds, 7, 9, 12, 15, 19, 25, 32 and 42 from start to finish. My timer has a metronome that ticks off the seconds so with a little concentration I can make strips on the test strip that have these exposures. I use an 11x14 mat board that is white on one side and black on the other. I set the timer for 42 seconds and step on the foot switch to begin the exposure. I expose the entire sheet for 5 seconds and the cover about 10% on the test with the white side of the card up, at 7 cover another 10%, at 9 seconds cover another 10% and so on to 42 seconds. This approach makes test increments that are easy to tell from one another and by exposing the entire test strip and gradually covering it resembles what would happen during an actual exposure.

During exposure, unfortunately, the light output is going to vary as the lamp warms. So making tests that start with most of the paper covered and gradually exposing more paper, as is advocated by most books, does not account for this change in light output. On the 5 second test strip the lamp would have been on for more than 35 seconds and would have a different light output than a fresh lit lamp. Using the approach outlined above, exposing the entire strip and gradually cover as time progresses will more accurately duplicate actual printing conditions.