EVOLUTION OF QUARTZ CRYSTAL CLOCK 



543 



P'ig. 16 — 100-Kilocycle quartz ring resonator with zero temperature coefficient. 



Fig. 17 — George Hecht iinishing the first set of zero-coefficient quartz rings. 



constant rate. All of these rings were constructed to have a zero frequency- 

 temperature coefficient at a temperature in the neighborhood of 40 degrees 

 C, the frequency being a maximum at that point on an approximately para- 



