Q. For calibration laboratories, what's the difference between a reference standard and a working standard?
A. A reference standard is any standard used to transfer traceability from a higher level external standard. For example, assume gage blocks are classified as class 1, class 2, and class 3 in descending order of accuracy. ABC Calibration Laboratory may send its class 2 gage blocks to XYZ Calibration Laboratory for calibration because XYZ Lab has class 1 gage blocks (which were calibrated by a national metrology institute such as NIST). XYZ Lab then uses its class 1 blocks to calibrate ABC Lab's class 2 blocks. These class 2 blocks would then become a reference standard for ABC Lab, which ABC Lab would then use to calibrate its own class 3 blocks (working standards). These working blocks will be used for calibrating lower accuracy hand tools such as micrometers and calipers. The class 2 reference blocks should only be used when the accuracy and/or uncertainty required for a given measurement is beyond the capability of the class 3 working blocks.