The piston is a relatively complicated component to measure because of it's oval shape and the resulting changes when being heated. It's diameter can be measured using a micrometer with an accuracy of between 0,05 to 0,01 mm. A micrometer for pistons having a diameter of 75 - 100 mm is shown in the above pictures 2 and 3. With each full rotation of the sleeve (50 division lines), the spindle moves 0,5 mm on the scale of 75 - 100 mm.
The compression height is the most important dimension of the piston. It is one of the factors determining the total height of the engine. Because 80% of the pistons mass is found in the area of the compression height, it influences the design and also the weight of the piston. A different value here of course, also changes the compression ratio of the piston engine. 07/11