The 1644-A will measure:

Insulation Resistance of cables, transformers, chokes, components, connectors, wiring, terminals, resistors, capacitors, relays, printed circuits, rotating machines, switches, circuit breakers, meters, strain gages, thermocouples, delay lines, slip rings, commutators, heaters, filters, lightning arresters, and other devices

Resistance of high-valued resistors, resistance films, diodes, transistors, and piezoelectric elements.

Voltage and Temperature Coefficients of resistance.

Volume and Surface Resistivity of solids, such as printed-board material, resins, plastics, potting and casting compounds, rubber, refractories, and semiconductors; of liquids, such as oils, plasticizers, and solvents; and of sheet materials, including plastics, recording tape, and varnished fabrics.

The circuit is a dc Wheatstone bridge with a high-impedance, high-sensitivity detector. Precision, wire-wound resistors are used for the fixed bridge arm and the lowest-valued decade-step arm. For medium values of the ratio arm, precision metal film resistors are used; for the highest values, carbon film resistors with trimmers. The balancing arm is a wire-wound variable resistor

The guard terminals eliminates the effects of stray resistances to ground. For capacitor leakage resistance measurement, charging time is a fraction of a second.