So, the issue w Doug's device is that the same blade point moves along the lenght of the string, not actually slicing, right?
Having said that, I will say outright that my two methods are the bouncing light maneuver, and the arm hair shave.
What I like to experience w the arm hair method is-as I move the blade along, the hair-all of it, easily pops off w little resistance.
I have recently started using the finger pad feeling test.
The paper slice is a good one that lots of folks use, has no risk of trauma....what kind of paper is the hardest to slice? Newspaper? Phone book sheets?