This resistance calibration board allows you to periodically verify the correct 2-wire resistance measurements of your tester, even after calibration, storage or relocation. We recommend checking once a quarter. A range of precision resistors and two diodes cover all 64 test points available on this board, covering values from 0.5O to 4.6MO. Manually move the card to additional banks and rerun the test to cover all test points. If you have expansion modules, you can order a CB48A Header Isolator™ Protection Adapter, Item 778A, to connect the board to expansion modules.