In Column E I have the data points for a straight, constantly increasing line which is called “Target”.

In Column C I have the data points for a jagged line (called “Actual”) that always follows the constantly increasing Target line, but the points are above and below the line.

Using 316 as an arbitrary number for example, when the two lines are plotted on a simple X/Y graph you can obviously confirm that, an Actual data point that is 316 units above (or below) the Target line is the same distance from the Target line whether it’s plotted on the left side (lower range), or the right side (higher range).

In Column D I can easily express the distance above or below the Target line in units, but I want to express it as a percent. So, to stick with the example, 316 units above (or below) the Target line in the left side (lower range) should be the exact same percentage as 316 units above (or below) the Target line in the right side (higher range).

I can’t figure out what formula I can put in Column D to deliver the % above or below the Target line, but if I pick any two “Actual” data points that are the exact same distance above (or below) the Target line, I want the distance as a percentage to be exactly the same (just like the distance expressed as units is exactly the same).

I think the solution is related to the fact that the data points in the beginning (lower left side) are relatively low numbers and as the time goes on the data points get larger and larger. Nevertheless, if I print my graph, identify two different “Actuals” that measure, for example, exactly 3 inches above (or below) the Target line, the distance expressed as a percentage should be the same.