7" Degree Wheel at Front Damper

I like it but I have a question. How is it indexed to the crank? In other words, how it it held in the proper position? The bolt holes will allow at least a few degrees of slop, so how are you keeping the wheel in check with true TDC for the proper reference?
It would mostly be for reference only. It wouldn't be a replacement for degreeing a cam while building. It would be good for checking an engine in a car you bought but didn't know anything about what's in the engine.