Note
QST, Apr 1947, page 15.
QST, May 1947, page 124.
QST, Jul 1952, p. 103.
MM-1 is a single unit with sensor and meter in the same cabinet. MM-2 has separate sensor and meter.
QST Mar 1954, p, 115 also mentions the MM-4 (52 Ω) and MM-5 (72 Ω) for power levels down to 2 watts.
See QST, Mar 1954 p. 115 for details on all versions.
Based on a construction article in the April 1947 issue of QST (and featured on the cover), by Mack C. Jones, (W1PNX). Jones' company almost immediately began commercial sales of the unit with an ad in QST the following month. The MM-1 was the first commercially available SWR meter. Later licensed to McMurdo Silver, which brought out it's on version in Aug 1947, the model 908.