Laboratory precision measurement of VSWR requires a calibrated Vector Network Analyzer, phase stable test cables, a calibration kit designed for the connector type you are measuring (which includes a precision 50 ohm load within it), and a test fixture for the particular connector type under test. If microwave frequencies, 100,000 USD is a rough price for that equipment. A little less for lower frequencies. If you don't do this sort of stuff a lot, better to send it to a Precision Measuring Equipment Lab.
For somewhat less precision, a Scalar Network Analyzer with directional bridge and calibration kit and Signal Generator is most often used. In both cases, the items in the calibration kits are traceable to a primary standard. They are housed in handsome, well crafted hardwood cases with custom foam inserts.