Type MD (1926 to 1934) Previous
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In the late 1920's as the meter companies incorporated improved compensations into meters to retain accuracy over wider temperature and overload ranges, Duncan revised their M2 meter to incorporate these improvements. This version is known with embossed or plain glass covers as well as a metal cover (similar to the M2's but without the DUNCAN embossing).

In 1929, several changes were made to the MD's design. The power factor adjustment was changed from the adjustable plate to a closed loop of wire. The cover was changed to a studless version with a pair of twist-lock bayonet joints (similar to the arrangement used on the later Sangamo HC meters). One version of the later MD was also made with a terminal box that could accept conduit fittings for a more secure installation.

Duncan MD
David Dahle collection