Some may already know about these, but I figured I’d share, just in case others haven’t.
My daughter gave me 12" and 24" center finding rules, and they are AWESOME. Not only do I use them free hand, but I also clamp them to my router and drill press fences, making centering holes, and routing stopped grooves easy.
There are several to be found by Googling, but mine are by Lance. Shipping took longer than she hoped, as they didn’t make it in time for my birthday, but hey, no issues.
-- Keith "Shin" Schindler