Oscillators and other frequency control devices specify their frequency variation in units of parts per million (ppm). The equation for this relationship is,
delta_frequency = (f x ppm)/ 10^6
where ppm is the peak variation (expressed as +/-),f is the center frequency (in Hz), and delta_frequency is the peak frequency variation (in Hz).
For example, 100 ppm of 100 MHz represents a variation in frequency(delta_frequency) of 10 kHz. The maximum and minimum frequencies are therefore 100.01 and 99.99 MHz, respectively.