Cheapest calibration checkbox on the market £19.95 for checking the calibration of instrumentation as required by NICEIC and NAPIT.The CalCard works as a Calibration Checkbox providing a range of fixed resistance's for confirming the operation of electricians insulation and continuity instruments. A fundamental requirement of "Part P" for domestic installers.To date the CalCard Ext1 has been viewed and accepted by IEE, NICEIC, NAPIT, ECA, IET and ELECSA to name but a few.