The Eyeball Test… and the Thumb pad test (TPT).

Trouble is it takes some time to calibrate your thumb to know when an edge is sharp. The benefit is you can test the whole edge, something you cannot do with hair. You are only testing the width of the hair. And it is a non-destructive test.

To calibrate your thumb touch every sharp edge you can, eventually you will know what a sharp razor edge feels like, start at the tip and work down to the heel.

Until then look at the edge, straight down with magnification. Any shiny spots are where the bevels do not meet and the edge is not completely sharp.

Once sharp, do 10-20 more weight of the blade laps to straighten the edge and begin the polishing of the bevel. This step pays large dividends at the next stone.

Here is a great video demonstrating the technique.