What is the most accurate Measurement Units the M1 can display?

The most accurate units that can be displayed (resolution) on the M1 Caliber is in mm mode (Metric) which gives measurements down to 0.100 mm (or 100 microns). 

In English units, inches decimal mode will be the most accurate down to 0.01 inches.

Note: The M1 Caliber's measurement accuracy tolerance is +/-.02" or +/- 0.500mm.

For more information about the different measurement modes, check out Measurement Units.