A thermometer is disclosed that utilizes a thermistor as a temperature sensor, to control the period and duty cycle of a multivibrator circuit. A second circuit, controlled by a microcontroller, measures both the charge and discharge times of the oscillation. From the ratio of these parameters, a precise indication of temperature can be obtained that is independent of temperature variations within the active components and the charging capacitor of the multivibrator circuit. The method is also independent of the value of the charging capacitor. Furthermore, by measuring the same ratio when a fixed resistor is substituted for the thermistor, a cell constant can be derived. The cell constant is used to calibrate the non-ideal response of the multivibrator circuit, thus providing a more accurate measurement of temperature.