adding time per division text to diagrams

When using diagrams and specifying the x axis as “Linear, number of divisions” it is difficult to determine the units/division when the x axis is “spread the x-range between cursors”.
I wish to provide a text box that shows the units per division ie(sec’s/div) and have it update when the zoom changes. Is this possible? I have not been able to determine the proper syntax.

OK, I was thinking if I used a formula containing the properties of the x-axis in the diagram I could do something like “(end value-start value)/ number of divisions”
I wasn’t able to get the syntax correct for the formula