Sharpening Angle Guide

I wanted to learn how to sharpen my chisels and plane blades by hand, but had the realization that it takes some practice to really learn the angles that you should sharpen a blade at. So, I figured a sacrificial piece of plastic would be a good way to do this, as I've seen something similar before. It's been a huge help for learning how to sharpen my blades and I figure it could be something that others could get a lot of use out of in training their hands to recognize the correct angle