"The NLS digital voltmeter Model 481 measures voltages rapidly and with a high degree of accuracy, and presents the measured value directly in numerical form on a self-illuminated digital readout. Digital voltmeters are, essentially, self-balancing potentiometers. Range changing and polarity indication are automatic, and decimal point and polarity sign are automatically displayed. This instrument is useful as a general puropse laboratory, production, and field test instrument, and is adaptable for use as a component of larger test systems. The advantages of the digital voltmeter are:

*** High Speed.

*** Its accuracy approaches that of laboratory type equipment while its ruggedness permits use under conditions in which most laboratory type equipment would not be operate.

*** Wide measuring range.

*** Numerical readings and automatic range changing and polarity indication features permit error free readings even with untrained personnel, and prevent instrument burn-out which results in other type of instruments when the range switch is ignored.

*** High input impedance at balance minimize loading of the circuit being measured.

*** High resolution. " (non-linear systems Model 481, Manual, 1960"

BRIEF SPECS

The model 481 is a lowcost voltmeter in the 1960 range. NLS called it an industrial voltmeter, indicating its possible use in industrial automation as a simple indicator unit. The better models V35 (5 digits) and V34 (4 digits) introduced one year after the 481 had pure transistor circuitry , printer output and oil-immersed stepping switches for higher reliability - but for a price tag of $ 3,750 resp. $ 3,150.

I actually do have two of these machines. The physical appearance is very bad, so I have to do an overall resoration. In general having a set of two is the best possibility for repair and continued service in future. Keep looking for such "twins" if you are collector.