Some time ago Durst made a test trip printer, where a strip of paper is pulled across a light-tight cassette a little at a time, exposing a slice of it to the same part of the image. I use it in conjunction of my Wallner timer system where five clicks on the dial makes a doubling of exposure time. I just run the paper across, and run through the Wallner's dial. This makes it possible that the selected samples are all consistent where the only variable is exposure time, and as each slice of the exposure corresponds to one run of the timer setting, the possibility of tolerance build-up by multiple exposures is also eliminated. It is odd that Durst did not produce this test strip printer for very long, but it is the only one which I think actually works in the sense of telling me what exposure (and with some analysis, filter number) I should use for making the print.