936 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



Fig. 7 — Photograph of the 7-inch oscilloscope with a typical gauging pattern 

 on the screen. 



The brightness control switch is used to compare gauging when the 

 relay is operating with the corresponding gauging when it is releasing. 

 An apparent difference of 2 to 3 mil-inches is noticed between the operat- 

 ing gauge point of a contact and the releasing gauge point. This measure- 

 ment change is ascribed to the tip flexure or follow of the contact wire. 

 Contact closure occurs when the contacts first touch, in advance of the 

 short follow travel during which the tension of the contact wire is 

 transferred from the card to the contact. In dynamic operation, the 

 contact opens when it is first struck by the card, before the tension 

 would be transferred statically from the contact to the card. Thus the 

 dynamic contact closure points agree with the static gauging, and differ 

 from the dynamic opening point by the amount of contact follow. Good 



