One more point about the HHT that I don't remember being mentioned: hold the hair at a 90 degree angle to the blade. I think this is assumed. But, a small amount of deviance can increase the cutting efficiency of the blade, giving a false positive.

To be more specific, when held at 90 degrees, the blade might cut hair with a slight pull. When held at 75 or 80 degrees, the hair might pop in two easily. This would indicate that the blade is sharper than it really is.

90 degrees. Always...