What are the absolute uncertainties of a micrometer and the vernier caliper?

This depends on the original specification of the device and upon it's current condition. Mechanical gage calibration deals with this all of the time, when they calibrate these devices against known standard fixed dimension gages. These reference gages also have uncertainty as well. But in general, good quality "thousandths" inch micrometers are typically good within about 1/3 of a thousandth across their entire range. Good quality "tenths" mics in good condition are expected to be within a ten-thousandth across their range. Good luck, Al K