a question from a newbie to PI

morning all,

first off i am relatively new to PI but i do have good experience with visual basic.

so my question

i am trying to plot a graph using 2 separate tag values. this would be point "X".  on the graph itself i would like a curve or line in the graph so i could see weither the point "X" is above or below the line and display a message depending on its position in the graph.

Any help would be greatly appreciated.

thanks in advance