Finding the Center of Cylindrical Stock

There are lots of ways to find the center of a round piece of stock, but *most* of them are a bit of a kludge and involve a combo square and more than two hands.  There are a few other "center finders" out there on the market, but this one is the easiest and most foolproof I have tried.  You can get one from Rockler Woodworking here : J Square Center Finder