Test Set I-49 is a compact, sturdy, portable Wheatstone bridge  incorporating a number of features recommended by telephone engineers. It is rapid in operation, light in weight, and small in size. Desingned for use in the field, all contacts are inclosed, the knobs are undercut, and the dial switches have positioning stops. The switches, keys, and binding posts are placed so that an operator wearing gloves can manipulate them easily. Connections for the various loop tests and for resistance measurements are made with a singel cam type key switch.
- a) to determine the location of a fault on a circuit,
- b) to determine whether or not a circuit is in normal condition,
- c) to measure unknown resistance,
- d) as an auxiliary resistance box
- Dimensions: 8,7/8 by 7,3/8 by 5,3/4 inches
- Weight : approximately 8 pounds
TM 11-2019 Aug. 1944 TEST SETS, I-49, I-49-A AND I-49-B AND RESISTANCE BRIDGES, ZM-4 AND ZM-4B/U TO 33A1-12-15-1