Getting transfer characteristics

[oshifis]

Maybe a trivial question, but I could not find a simple answer:

Taking the curve family of a tube (triode, pentode) and for a given load line, how can I determine the output current versus input voltage curve?

In other words: I have the anode current versus anode voltage curve family, where the parameter is the grid voltage. Now I draw a load line on the graph. It intersects the curves, and at each intersect point I can read the anode voltage and anode current for some discrete values of grid voltages. My question: how can I graph the anode current (or anode voltage) when the variable (x axis) is the grid voltage?

[Bandersnatch]

hey-Hey!!!,
Try transferring points to excel, then curve fit to get points in between.
cheers,
Douglas