Gauge blocks are calibrated at 20°C. At 23°C the uncertainty of steel blocks would be approx ±1500nm. Stacking blocks increases the uncertainty and potential errors. The guys in the cal lab never stack more than 2 blocks
If I need an accurate block I machine a 20mm diameter round bar in the lathe and check it with a micrometer Zeroed at whatever temperature I am working at.
If I need an accurate block I machine a 20mm diameter round bar in the lathe and check it with a micrometer Zeroed at whatever temperature I am working at.