Review on Mitutoyo 050103 Center Finder Diameter by Brock Chisholm

Simple, well made and accurate. It can find the center of the hole or find the edge. And unlike LED-based edges, it works on metal or non-conductive plastic blanks. And because the tips are spring-loaded, it's much harder to bend them by accidentally turning the lead screw the wrong way. No battery is required either. Sometimes low tech is better.