On the dyne pens, they come in different numbers. You can get them up to 70 and they start in the lower 30s. If you by a package of dyne pens you get an array of numbers. DI water on a clean surface should be about 72 so we always look at that one for cleaning but if it passes below 72 you could try a 65 or a 60. The kit you get should come with an array of solutions for testing.