This set comes with calibration certificates traceable to NIST that state each tool has passed a test for accuracy. It includes a dial caliper, a micrometer, a ruler, and a case. The micrometer has a ratchet thimble with a constant-force mechanism, which stops the spindle from tightening once it contacts the surface of the measured object. This ensures repeatable measurements and prevents over-tightening. When the spindle stops tightening, the thimble will continue turning with a clicking sound. A speeder knob reduces the time it takes to open and close the micrometer.