QC Lesson of the Month


James O. Westgard, Ph.D.
Sten Westgard
Paul Schilling

August 1999

See QC - The Calculations for an explanation and equations for these calculations.
See QC Calculator Problem Set if you want to work with some sample data.

 NOTE: These Javascript Calculators only work on browsers that support Javascript!

Fill these blanks in if you want to print out a hard copy of your data after you enter it
Control Material  


Monthly Mean, Standard Deviation & CV

Enter up to 40 measurements, then click the buttons to obtain the calculated values for the mean, standard deviation, and CV. Blank entry boxes are not included in the calculations but zeros are.



Cumulative/Lot-to-Date Calculator for
Mean, Standard Deviation, and CV 

To calculate cumulative control limits, enter the previous month's figures for n, sum of x, and sum of x squared, then push the "Total" button. To calculate monthly control limits, just push the "Total" button and only the monthly figures will be used.  

See QC - The Calculations for more information about these calculations 
Previous month's 
(or months') data
This month's data

Sum of x
Sum of x2






Control Limit Calculator

Note that you can re-enter the multiplier for the control limits to use the calculator for more than one control limit. 

Enter the control mean: 
Enter the control standard deviation:  
Enter the control limit you wish to evaluate 
(enter the multiplier number only, i.e. 2, 3, 3.5, etc.):
Once you've entered these three values, click this button to calculate your limits 
Your Upper Limit will appear here:  
Your Lower Limit will appear here:  


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Westgard QC, 7614 Gray Fox Trail, Madison WI 53717
Call 608-833-4718 or e-mail westgard@westgard.com

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