Carl Goldberg models used to come wioth a center marker. Since then you have been able to buy them. Great little tools.

GP came out with one recently, that is a little over engineered in my opinion, but does the job.

If you have a steady hand, you can make pretty good oens with just an X-Acto knife. Just takes time!

Then someone thought of teh idea of mounting an X'Acto blade on a riser / a small block, to be at the right hieght, and then either puch teh surface, or push the blade & riser into the wood.. Works well, and is repeatable..

Then was the 'V' tool tht we're all talking about. came with a fancy 'cenetering' jig. Nice touch. Push teh 'V' into the wood, and it came with a 'gouger' to remove material. Still have mine... Still use it too!

Then, recently, someone developed the 'powered hinge slotter'. My buddy bought one. He loves it. I... well.. I prefer teh 'V' tool. I find teh thing jumps around too much, is loud, and is really just a gimmick. But for hard woods, it is a nice thing to have..