The resistors are of manganin coils bridge wire is accurately calibrated. Vernier is attached to the sliding contact and fine slow motion available mercury  contacts are fitted. Length of the slide wire is 30 cm. Resistance values are 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4, 12.8 and  0.15 ohm for 30 cm slide wire. Range of resistance measurable.