How to know when your edge is "sharp" enough

[MauleSkinner]

Shaving hair is a fashion statement…some of us are all about image.

[Timberwolf]

Shaving hair is a fashion statement…some of us are all about image.

............
Right...Some of us can't help being a chick magnet...

[Ricky]

Not necessarily. I used to shave arm hair, but not anymore. My 80 years have reduced my body hair to almost nothing, and I am protective of the little I have left. I learned that if I present an edge to the flat of my fingernail with no pressure other than the weight of the tool, it will skitter off if it is dull. A sharp edge will catch immediately. I do this several places along the edge to make sure I've got it consistently sharp along its entire length. It works perfectly and does not waste hair or deface my arm.

I do this when sharpening kitchen knives on stones at the kitchen sink.  Copied this from Murray Carter.   He also does the finger tip testing along the edge but for now I'm comfortable with the fingernail.