Also when you're doing test-strips, you often want to see the effect on one small critical part of the print, e.g. a face or a particular shadow so a strip which distributes the measurement steps across the image is often not appropriate. What I prefer to do is make a bunch of test-tiles and expose each of them individually at the test times. The time taken to do this is obviously longer than incrementally exposing a strip but IMHO it gives you much more-useful and more-consistent results.