RELIABILITY OF HOLPIXG TIML M EAST REM EXTS 



395 



switch counts at finite inlcrxals. Heme on V'v^. 18 is shown tiie o\erall 

 error distribution for the illustrative example given above with the dis- 

 tributions of its two elements as well. The method of combining standard 

 deviations (equation (vM)) explains why the two error distributions of Fig. 



0.5 1.0 1.5 2.0 2.5 3.0 



Z= ERROR IN MULTIPLES OF THE 



THEORETICAL STANDARD DEVIATION 



1 2 3 4 5 6 



ERRORS IN PER CENT OF OBSERVED 



(a) (b) 



Fig. 17 — (Comparison of observed and theoretical overall errors 



12 3 4 5 6 7. 



ERROR IN AVERAGE HOLDING-TIME ESTIMATE IN SECONDS 



Fit;. 18 — Typical overall distribution of errors in estimating average holding times 



18 do not add directly to give the overall error curve. We may immediately 

 draw the important conclusion from Fig. 18 that the errors due to the uncer- 

 tainties at the ends of the observation period may in certain cases be con- 

 siderably greater than those due to the lack of precise measurement of the 

 length of each individual call. 



