Just select your data and QI Macros does all of the calculations and draws the control chart for you. QI Macros is an easy to use add-in for Excel that installs a new tab on Excel's toolbar.

Instead, use proven software like QI Macros Add-in for Excel Software! You can try and calculate sigma and the control limits yourself, but. Montgomery * The secret formula to ignoring all other formulas. * 'Introduction to Statistical Quality Control,' Douglas C. Here are some examples of control limit formulas: There are seven main types of control charts (c, p, u, np, individual moving range XmR, XbarR and XbarS.) Plus there are many more variations for special circumstances. The formula for sigma depends on the type of data you have:Įach type of data has its own distinct formula for sigma and, therefore, its own type of control chart. Why are there so many formulas for sigma?

± 2 sigma and ± 3 sigma from the center line. The formula for sigma varies depending on the type of data you have. The Center Line equals either the average or median of your data. The secret formula that helps you ignore the rest!