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Hmmmmm I agree but not in full, You would have to do an HHT every 1/4 inch to be sure of that,,, So although yes I agree it can be used, I don't agree that is very effective....
And the other...

A low grit HHT on a razor means nothing, in fact most of the time it is easier as the rougher edge catches the hair...

The HHT has to be developed into a useful test just like every other test...