Adding a "Slope" Calibration Mask to your CUSUM chart

For the aid of the viewers of your CUSUM (or your own reference) it is useful to add a calibration scale to the CUSUM. Remember that with a CUSUM its the slope of the trend that conveys the average, and changes in slope that indicate increases or decreases in the underlying data.

The simplest way to add the scale is to add a few series (typically 3) representing reference values for a short period at the beginning of the graph. It might look something like this picture.


To generate values for the series, simple use the same CUSUM method on the calibration value, using the same mean that used previous to generate the CUSUM.

For example, the CUSUM slope for the value 5 might start like this in column G:

[Cell G4] = G3+5-$B$3
[Cell G5] = G4+5-$B$3
where $B$3 is the mean you calculated previously.

Here's the example spreadsheet.

Happy charting!