There is no way to set marker(s) from FPScript, but there are other ways to achieve the same goal.
Let your FPScript formula extract the desired points as a signal. Add it to the diagram. Using the Properties window of the new curve, switch off the [i]Connection Line[/i] and activate the [i]Data Labeling[/i]. In the [i]Text[/i] field enter
[b]Y = %
X = %[/b]
(you may add some formatting too, e.g. %.3f for three decimals).
Change the [i]Angle[/i] to 0°, the [i]Position[/i] to [i]Top Right[/i] and the [i]Background[/i] to the desired color. If you want to see the points too, turn on the [i]Symbols[/i] and choose the appropriate [i]Type[/i] and [i]Color[/i]s.
