The Calibration Checkcard CalCard EXT1 works similar to the more commonly termed "Calibration Checkbox". It provides a range of fixed calibration resistance's for confirming the operation of electricians insulation and continuity instruments as per NICEIC resistance checkbox.. This is a fundamental requirement of "Part P" for domestic installers.

The CalCard EXT 1 calibration checkbox is currently been used by hundreds of Part P registered tradesmen who have been certified and their records checked by inspectors against measurements using the Calibration Checkbox CalCard Ext 1.

These professionals are members of various institutes and recognised bodies. To date the Calibration Checkbox CalCard Ext1 has been viewed and accepted by IEE, NICEIC, NAPIT, ECA, IET and ELECSA to name but a few.