This disclosure relates to controlling an oscillator based on a measurement of a frequency reference. A controller determines a control value to control the oscillator based on multiple error values. Each error value is indicative of a measurement of a frequency difference between the oscillator and a frequency reference over a period of time. The determination of the error value is further based on an application time value indicative of a time of application of the control value to the oscillator. Since the control value is based on the application time the controller can compensate for inaccuracies arising from both evolution of the oscillator between measurements and applying the correction at a later time after the measurement. Further, since the multiple error values represent a frequency difference over different periods of time, the controller can compensate for wide range of statistical effects.