How does temperature affect a micrometer?

Answer 1

All materials change size with temperature. Some more than others. While this is usually so small as to be unimportant, when working with a high-accuracy device like a micrometer, it can make a big difference. After all, you're using a micrometer instead of a ruler because you care about small differences in size/length.

Micrometers are usually calibrated for use at 20 °C (68 °F). Put the micrometer and what you're measuring into a temperature-controlled room at 20 °C for a couple hours before taking measurements. (Longer is better, especially for super-high-accuracy measurements.)