Brian from "
bootheel customs" has created the "Ultimate All-In-One Angle Tool"...

... that is used for setting the USB height, (for setting the angle in knife sharpening). It measures the Wheel Diameter, Projection Distance, and then, (with the aid of a calculator), sets the USB height
measuring directly to the wheel. I've used one the last week or so, and found it to work well.
Edit: The All-In-One Angle Tool is now sold
HEREEdit:
A newer (& shorter) YouTube Instruction VideoAn older
YouTube Video, showing it in use.
(p.s. Not affiliated BTW, just like it).