An apparatus and method improve the accuracy of measurements taken with a capacitance-type sensor. In addition to the sensor the apparatus comprises a measurement circuit and a microprocessor. One of the sensor or a calibration capacitor with a known and fixed capacitance is connectable to the measurement circuit by a switch that has its position controlled by the microprocessor. The microprocessor sends measurement signals to the measurement circuit and receives data therefrom. According to the disclosed method, the measurement circuit is programmed to determine an error between measured calibration data and the known capacitance and to use this error to calculate a correction value, which it applies to the measured sensor data to calculate corrected sensor measurements.