Allegro field computers come with an integrated digital voltmeter (DVM) that we recommend our customers calibrate every twelve months. To find out when yours was last calibrated, open the unit and check the sticker on the DVM. If your DVM hasn't been calibrated in the last year, send it in and we'll use industry standard, NIST-traceable calibration equipment to make sure it's in peak condition by checking parameters like AC and DC voltage.
The whole calibration process typically takes only a week, though it can take up to two weeks during peak seasons. After the calibration, you'll receive a report showing detailed test data that you can present to your auditor upon request (here's a sample report).