When a crystal unit is actuated as an inductive reactance in an oscillation circuit, the relationship between crystal unit and oscillation circuit is shown in Fig.6.To improve the starting conditions of the oscillation circuit, it is preferable to increase the value of negative resistance -R which parameter of the oscillation circuit .The starting conditions will become worse if a circuit without much allowance in negative resistance (less negative resistance )is combined with a crystal unit having a larger resonance resistance. The oscillation circuit should be designed to a goal such that the value of negative resistance is 5 to 10 times the resonance resistance. It is also necessary that the center value of load capacitance (to determine the absolute value of oscillation frequency )and the variable range (fine adjustment range of oscillation frequency) are maintained at the optimum values in the oscillation circuit.