This method of finding the center point of a circle is Thales Theorem, which uses the outside of the circle instead of the inside of the circle. It is the fastest way I know of using tools that most people have in their tool arsenal.

Markal Silver Streak - https://amzn.to/3ntlNAo
Starrett Combination Square Set 12" - https://amzn.to/3nvTQYS