Product Description The RS-500 resistance substitution box is a convenient instrument for determining the desired resistance values In circuits under design or test. The resistance obtainable is from 1 Ω to 11, 111, 110 Ω in 1 Ω steps. All resistors are precision 1% resistors. From the Manufacturer 1% 1W Resistor Substitution Box Model RS-500 - The RS-500 Resistance Substitution Box is a convenient instrument for determining the desired resistance values in circuits under design or test. The resistance obtainable is from 0 omega to 11,111,110 omega in 1 omega increments. All resistors are 1% precision, 1 watt resistors.