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BELL SYSTEM TECHNICAL JOURNAL 



Fig. 15.13 — Exterior view of crystal Performance Index meter. 



15.83 Frequency Errors 



As suggested in Section 15.81, conformal representation simplifies the 

 mathematics required for the determination of frequency errors. In Section 

 15.81, the difference between the resonant frequency and the minimum im- 

 pedance frequency was computed for the equivalent crystal circuit. This 

 same procedure could be used to compute the frequency difference between 

 the antiresonant frequency of the generalized oscillator circuit (Fig. 15.2) 

 and the minimum impedance frequency of the P.I. meter for the same value 

 of Ct. Comparison of the frequency of these two oscillators is plotted in 

 Fig. 15.6 together with the measured values obtained from a 'Tierce" and 

 a "Tuned Plate" oscillator. This frequency comparison involves setting 

 up two circle diagrams, one for Zab (Fig. 15.2) and one for the impedance, 

 Zi (Fig. 15.3) similar to Fig. 15.10. The impedance equations for both Zab 

 and Zi would be arranged such that they have the same function of Z in 



