Review on TM8812 Ultrasonic Thickness Gauge: Accurate Measurement from 1 to 200mm (0.05-8-inch) by Johnny Chambers

Worth the money to check the cylinder block as it's cast iron. Calibrate with the steel block turned on, then toggle the material mode. You will find that checking the calibration block with a gauge with a different material setting will not give a calibration value since the block is made of steel. So you know it balances the choice of material. I did the first accuracy tests on gray cast iron surfaces, which I was also able to measure with a caliper. It has decent accuracy even if the surface isn't finished. +/- 0.010 on cast surface. I found this to be within the specified tolerance on machined surfaces. Cannot be read when recording irregularly shaped objects or too close to edges. IE The extreme upper and lower parts of the cylinders where the transition of the casting material takes place. Once I figured this would work, I modified the sensor to match the curvature of the block for easier sensor connection. I put sandpaper in the hole and carefully sanded the sensor to a rough shape. Keep the center divider in line with the length of the cylinder. Enough sand so that the clutch fluid can take up space more easily. I used an all purpose lube called glycerin which works well in any position. The manual recommends oil, but the thicker glycerin seems to work well.