Abstract: Apparatus which provides a digital signal which represents the unbalance in a resistance bridge. The apparatus includes a source of direct-current voltage which is applied alternately and repetitively with opposite polarity to input terminals of the bridge. An amplifier is connected to the bridge output terminals. Analog-to-digital converters are connected to the output of the amplifier in such a way that one converter is connected to the amplifier output at a time when a positive voltage is applied to the bridge input and another converter is applied to the amplifier output at the time that a negative voltage is applied to the bridge input. A count is provided which represents the difference in the digital signals provided by the two converters. Such output is unaffected by any initial unbalance in the amplifier and is also not responsive to thermo-electrically generated electromotive forces.