Humboldt State University
Robert A. Paselk Scientific Instrument Museum
Weston A.C. Ammeter, Model 155
Weston Electrical Instrument Corp.
Humboldt S-T-C; c.1926
Instruments such as this were used by trained technical/scientific staff for precision laboratory measurements of electrical current, and as secondary standards for calibrating other meters. The mirrored scale makes it easier to read the instrument to a given accuracy by enabling the user to eleiminate parallax errors. This particular instrument was specified to be accurate to ±0.5%.
The instrument in housed in a 71/8 x 6 3/4 x 3 1/4" walnut case with a leather handle. All hardware is nickel-plated brass. The front panel has a window cut into it to view the meter face. The meter has a mirrored scale. The serial number (52947) is hand written on the white paper scale behind the face plate. Only one of the two screws in the side of the case allowing access to the movement is sealed with black sealing wax(?) and stamped with a "W," the other seal has fallen off. The instrument has four rubber feet on the bottom for storage and four more feet on the back for use during operation. There are two nickel-plated brass binding posts on the left side of the instrument's case.
Beneath the window is a brass escutcheon labeled "0 CORRECTION" giving access to the zero correction screw. There is a brass plate finished in black and nickel plating attached to the front of the cabinet below the escutcheon:
An oval brass tag attached with brass brads to the left side of the instrument is stamped: HUMBOLDT S-T-C / 2099. The original finish is crazed and chipped around corners and edges. Exposed metal parts are generally corroded with a black nickel patina. The leather handle has been oiled and is still strong and flexible. The case has been lightly cleaned and waxed.