Camshaft timing when the sprockets are ONE tooth off from straight up.

I was taught to check if a timing chain had jumped a tooth (particularly cheb plastic gears), that to put #1 or #6 (or#1or #4 on 4 cyl. cyl) in equal overlap.
If the timing mark was more than 12*, the chain had jumped, not stretched.
Proved true time and again.
That was my test