380400 Resistance Decade Box | 7 RangeThe Extech 380400 Resistance Decade Box is used for product design testing and calibration which can be substituted into a circuit and function in the place of any component with a standard value. Alternatively, it can be used to identify the best value for circuit operation then read that value from the switches. A resistor of the size indicated by the decade box switches can then be put into the circuit.