SHEET NON-FERROUS METALS 



797 



silver plotted to show directly the differences between readings on 

 the two machines of each type, one being assumed as a standard. 

 Figure 21 shows the frequency of occurrence of the various degrees 

 of difference between the two instruments, giving results for both 

 the Rockwell and the scleroscope. One of the instruments was taken 

 as a standard and the variations of the other instrument from it are 

 plotted to left or right as they are negative or positive. The fre- 



100 



^90 



•< 

 o 



80 



70 



60 



I 



50 



40 



POINTS REPRESENT — 

 SPECIFICATION LIMITS 

 TEMPER MIN.MAX. 



+ X 



i HARD 

 •J HARD 



|- HARD 



HARD 

 EX.HARD 



SPRING A A 

 EX.SPRING A A 



o 



30 



50.000 60,000 70,000 80,000 90,000 

 TENSILE STRENGH -PSI 



100,000 110,000 



Fig. 23 — Comparison of Curves of Results from Experience Data with Limits 

 Adopted, for High-Brass Sheet. 



quency of occurrence of differences of the magnitudes represented 

 by the abscissas are plotted as ordinates in per cent of the total read- 

 ings made on the group of samples for which the curve is drawn. 

 In this typical case it is seen that about 50 per cent of the Rockwell 

 readings from one machine are 4 points below those from the other 

 machine. Application of a conversion factor would, therefore, move 

 the curve to the right 4 points and very close checks between the two 

 machines would result. The scleroscope curve shows that readings 



