Hole centering aid

[Toolguy]

The great thing about it is that you don't have to measure the chord, or worry about it. If you're close to center in X, each end of the chord will be centered in Y. The slightly angled part isn't an issue. I've been doing it this way for a lot of years and checked it out with a dial indicator several times. It's always close enough for my jobs. Maybe it will work for you, too.