Practical Electronics/Oscillators

Crystal Oscillator provides an Oscillator
 * f = nfo

Using LS tuned tank
 * $$f_o = \frac{1}{2\pi} \sqrt{\frac{1}{LC}}$$

The "negative resistance test" measures the oscillation allowance of a crystal oscillator circuit. Most manufacturers recommend that the oscillation allowance of the circuit be at least five times the maximum resistance value of the quartz crystal unit used in the circuit.