schlink: variance of measuring instruments 



399 



alterations of the weight of the pendulums and of the contour 

 of the cams about which the load transmitting tapes wrap, 

 while the width of the hysteresis loop gives a good index to the 

 workmanship of bearings and connections. 



Backlash an important cause of variance. In a measuring 

 instrument the maintenance of constant or at least determinate 



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F'g. 1. Hysteresis loop of automatic weighing scale of the cam-pendulum 

 type (comprising no elastc force-measuring elements). Note the manner in 

 which the curve of decreasing readings reflects the aberrations of the curve of 

 increasing readings, w'th a distinct tendency toward wider separation at the 

 middle of the oad range, so that the hysteresis loop would have a distinctly lentic- 

 ular form, if the median line or mean error curve were rectilinear. 



intervals between the parts of the mechanism is essential in the 

 transfer of the forces or motions from the point of their reception 

 to the point of registration or indication. Slack or backlash in 

 the mechanism has the same effect as an equivalent advertent 

 displacement of operating parts, backlash being used to imply 

 looseness of fit resulting in play of the coacting parts. Actually, 

 the action of backlash is not the simple one of producing a hystere- 



