In the radio world we use the quartz crystal to construct a crystal oscillator. The vibrating crystal generates a sinusoidal electronic signal on a precise frequency.
The modern radio receiver uses a 10 MHz quartz crystal as a reference for the frequency synthesizer for the tuned frequency.
Crystals must be custom tuned by cutting or grinding to exact dimensions and tolerances to achieve a highly accurate desired frequency.
Crystals marked P-77 are for radio shack scanner with 10.7 IF