Gauge block
most command with ceramic and tungsten steel that available in our market for 
mitutoyo gauge block
Is a wide range of use for precision instrument verify purpose.
a simply way to make sure the instrument condition after a high usage
it helps to setting your machine with less than 1 micron measurement accuracy
not only for measurement, gauge block formally know as a CNC machine preset use to avoid program mistake to make a crash
please remember apply a anti-corrosion oil to protect the gauge block after contact with skin. it could be rusty if do not apply the oil, especially the high humid environment
at last, the room temperature are so important when you need accuracy with just less than 1 micron, the result could be getting bigger rather than actual due to high temperature expand.