Kevin is correct. The other thing you can do is to calibrate it on a portion of what you are testing. For example, just use a caliper to measure the china wall on a block, and compare that to what the sonic checker tells you. You can also do it on the areas between the bores. I like checking it on the actual piece because the calibration standard built into the checker uses a different material than the cast iron we normally use, so the setup on the sonic checker is different.
