This is nearly identical to my previous version, found here. I added 12 tick marks that cut into the surface and are easy to track along the outer diameter. This way, when taking measurements, you can be sure you're pretty much in a straight line.

I also added .5mm thickness. Even though it's for dimensional accuracy - and, I suppose, height accuracy - measurements, the previous version at 2mm felt a little too insubstantial for my tastes.