1. A method of generating a time-base signal for timekeeping, comprising the steps of: storing adjustment data in a non-volatile memory; generating an oscillator clock signal having a certain oscillator frequency; counting said oscillator clock signal cyclically with a first cycle length, said first cycle length being programmable, thereby repeatedly generating a time-base cycle; setting said first cycle length to a nominal value; setting and resetting said time-base signal once in each said time-base cycle; counting said oscillator clock signal cyclically with a second cycle length, said second cycle length having a fixed value greater than the nominal value of said first cycle length, thereby repeatedly generating an adjustment cycle; adjusting said first cycle length by a certain total amount, determined by said adjustment data, in each said adjustment cycle; and restoring said first cycle length to its nominal value in each said adjustment cycle.