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REGULAR CALIBRATION INTERVALS HELP ENSURE MICROMETER ACCURACY. BY NOBUO SUGA
The inventor of the modern micrometer, Jean Laurent Palmer, introduced the basic principles of magnification based on screw threads. His design is based on a 1-millimeter, single-pitch open screw thread. One rotation, or 1 millimeter, was divided into 20 equal parts, bringing the smallest resolution to 0.05 millimeter. His design was so advanced and complete, that nothing has been added to or subtracted from his original concept in terms of the principles of operation.
To ensure accuracy, micrometers must be calibrated at regular intervals.
The 4 to 1 rule
* The standard used in calibrating measuring gages must possess an accuracy greater than a 4 to 1 ratio over the accuracy of a gage being calibrated. This common rule of thumb originated some 40 years ago from MIL-STD-45662A, which was first published in 1960. A gage block is used to calibrate an unknown micrometer. The "unknown" is the micrometer and the "known" is...