Abstract: Variations, due to aging, of resonant frequency characteristics of electromechanical resonators are compensated by an oscillator including the resonantor. An indication of the amount of time that the oscillator is operating addresses a table of values indicative of the manner in which the oscillator changes frequency as the resonator ages. From the table of values a signal having a value indicative of a correction factor for the resonator aging is derived. The frequency of the oscillator is controlled in response to the value of the correction factor. The table of values is stored in a re-programmable memory. The values stored in the memory are corrected by comparing the oscillator frequency with a standard frequency.