Centerfinder

My grandad had a very handy tool laying around, a so called: Kell Centerfinder.It's a little tool that lets you determine the exact center of a round object.

How to use it?
Just place the two 'pins' against the edge of a round object and draw a line. Than turn it about 90 degrees and draw another line. There you go! You should have a cross at the precise middle of your object.