Crystal oscillators are loosely divided with the frequency they get the job done at and whether they are elementary oscillators—function within the frequency marked about the can or at even multiples of that (overtone oscillators). As you'll be able to see with the graph below, crystals have two resonant factors. https://ledbookmark.com/story4598545/how-bulk-crystal-oscillator-can-save-you-time-stress-and-money