unusual behaviour when graphing

[Mickpc]

I am graphing using the following program:

EXPORT Is,Vd,Vt,n;
EXPORT SHOCKLEY()
BEGIN
'I=Is*(e^(Vd/(n*Vt))-1)'▶E1;
1▶n;
10ᴇ−12▶Is;
26ᴇ−3▶Vt;
0▶Xmin;
0.8▶Xmax;
5▶Ymax;
0▶Ymin;
STARTAPP("Solve");
END;

When I run the program, select and solve for Vd (to set the independent variable) then plot the program I get a line across the x-axis as well as the exponetial curve. It seems there are two curves.
I have cleared all other equations out of the solver and the graphing app.
Anyone have any ideas?

Also is it possible to set and solve for Vd from within the program? Instead of going into num and manually selecting it?

King regards

Mick C

HP Prime A Gentle Introduction