Read values from plots

If I understand the request correctly, you want something like this?

(This uses Horizontal and Vertical markers where the vertical marker is equal to xvalue and the horizontal marker is set equal to xvalue². xvalue can be slided with the Slider control that goes from -10 to 10. Doing this changes the location of both markers)

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@DJNewman wrote:

Very cool incremental improvement.
Question; in the hidden area you use a -x- notation in your definitions. What does that mean/do?

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Using -x- and also -f- and -ff-  was just an attempt to choose variable/function names that are highly unlikely to be used in a normal sheet, as names containing a minus sign cannot be generated by normal means.
Doing this was quite unnecessary here in the demonstration example and was also counteracted by the introduction of the TraceXY vector. 😉

Actually I introduced TraceXY because I thought that the labels in the markers could not show more decimals (they could using the normal math format) and so I would be able to show the 'cursor' position with more precision. It was just later that I realized that it was the slider which only provides coarse values and I found that using the Slider.TickFrequency(...) method allowed to use a more refined grid of values then the setting in the properties tab. Unfortunately this does not help much because the slider reacts very slowly and imprecisely. Wish this could be improved and that we could move the slider using the keyboard in much finer increments.