If you are going to cut down a prop, Jim has a neat tool for marking them also. It works off the center hole and marks both blades exactly the same. Cut the blad a little long and sand down to the line , reshape and balance. Good for checking existing blade length against each other if you suspect the hole is off center, and I have seen that happen many times. The magnetic balancing stand that Great Planes offers, when modified with shorter connecting rods and used with their finger tip balancer instead, is very precise and helps detect misshapen center holes, and bad blades.
Good luck and have fun,
Dan McEntee