FAQs

How can I determine the maximum or minimum value in a set of variables?

There are many scenarios in which it is helpful to know which variable in a set of variables contains the largest value. Similarly, there are many scenarios in which it is helpful to know which variable in a set of variables contains the smallest value. These scenarios can all be addressed by using WinSPC's Equation Builder to calculate maximum and minimum values. The following procedure explains how to do this.

1. Set up the set of variables within which you want to determine the variable with the maximum or minimum value. (Note: In most cases, each variable in the set will have the same specs, settings and control limits. Otherwise, the maximum or minimum value risks being relatively meaningless.)
2. Create a new variable for the maximum or minimum value.





3. Double-click this new variable and, in the Variable Setup dialog box that appears, click the Advanced button.
4. Configure this variable to have the same specs and settings as those in the set of variables.
5. On the Settings tab, click the Calculated check box and then click the Equation button.
   
   
   
   This causes the Equation Builder to be displayed.
   
   
   
   
6. In the Calculation Text area of the Equation Builder, enter an equation that will compare the values in the variable set and identify the maximum or minimum value. For the maximum value, an acceptable equation will look something like this:
   
   
   
   For the minimum value, an acceptable equation will look something like this:
   
   
   
   In these examples, there are three variables in the variable set: V1, V2 and V3. For larger variable sets, the pattern illustrated here can be extended as necessary.
7. Click the OK button in the Equation Builder.
8. Click the OK button in the Variable Setup dialog box.
9. Add all the variables, including the calculated maximum or minimum variable, to a collection plan.
10. Load the collection plan into the Data Collection window and collect data for all but the calculated variable. WinSPC will then determine the value for the calculated variable. 

As an aside, if you want to calculate the range for a variable set, you can build on the concepts introduced above and use an equation similar to the following:

Maxvalue = V1
If V2 > Maxvalue Then
   Maxvalue = V2
End if
If V3 > Maxvalue Then
   Maxvalue = V3
End if

Minvalue = V1
If V2 < Minvalue Then
   Minvalue = V2
End if
If V3 < Minvalue Then
   Minvalue = V3
End if

Result = Maxvalue - Minvalue