That's very much appreciated! Engineering goodies are great to have. But like on brian6pac's unit, this sonic gauge comes with a disc of calibrated thickness built into the side of the case.
And I checked this gauge against a brake rotor because it is cast iron, and I wanted to make sure I knew how to set the gauge up for the different material velocity. The sonic velocity through cast iron is about 20% lower than steel so you have to be sure to set it up right, or the results will be waaay off.
