Sharpening for task.
Then once you know what that "sharp" is, find other methods with that "sharp" and get a "control" or "base".
i.e. Sharpen , shave arm, and see how that edge does with fingernail, or matchstick, toothpick, tomato, grape, drinking straw, plastic disposable ink pen...or pull a hair from your head (or use a dawg hair from the chair) and whittle it.
True.
Second wife was using a carton cutter, and the single edge razor blade was "used" and not cutting well.
I happen to walk in, and used my Boker 240, with rosewood handle, and carbon steel blade, to cut what she needed cutting.
"Babe, that sucker is sharp!" she said.
She knew I kept a sharp knife, and she knew how to freehand sharpen, still it surprised her.
I grinned, as I had just stropped that knife on my belt, just earlier. I suggested she whittle a dawg hair...
She snagged a dawg hair, and caught the sunlight just right, and my pocketknife whittled that dawg hair.
She had always just checked her sharpening on a matchstick, or tomato, or grape.
4 pound test fishing line, is easier to hold onto and see, so there is another way to test.
2 pound works, just most folks find the 4 pound is easier to use.
That said...
You may not need a knife "shaving hair sharp" for some tasks.
i.e. cutting rope.
Convex edge using emery paper on a magazine, or mousepad and say 180 -200 grit. Coarse side of a Norton stone, or coarse Eze-Lap diamond.
Sometimes coarse "toothy" has its place. While it won't shave arm hair, it will cut for tasks.
