What measuring equipment should I use for specific tolerances?

For measuring longer parts, a combination square or ruler can be a good, quick option. Measurement error is probably around ±0.10”.

Calipers can be used for many general uses, where a tolerance of ≥ 0.002” is acceptable, even though they often read out to ±0.0005”. Things like slop in the jaws, abbe error, and measurement repeatability (how hard you “squeeze” the calipers) make the measurement error higher than the readout precision of the calipers.

For more precise measurements, micrometers can be a good option as they typically have a tolerance of ±0.0001”.