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In order to confirm whether ample oscillation allowance has been provided for the oscillator circuit or not, it is necessary to find out the negative resistance (-R) of the oscillator circuit.


Insert, as shown in Fig.1 a variable resistor (VR) (for checking) in series with the quartz crystal unit. Then keep dropping the resistance until oscillation initiates. (In this case, disregard the drop in the oscillation output, and merely confirm oscillation.)
The negative resistance (-R) of this circuit, is the value obtained by adding the equivalent resistance of the quartz crystal unit to that of the variable resistor (VR) (used for checking).

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iii. To assure the provision of an ample oscillation allowance for the oscillator circuit, adjust C1, C2 and Rd?? so that the resistance of the variable resistor (used for checking) becomes 5-10 times larger than the equivalent series resistance (CL value) of the quartz crystal unit.