HP 39gs User Manual page 262

S1fit...S5fit
Statistics
18-40
Sets the type of fit to be used by the FIT operation in
drawing the regression line.
From Symbolic Setup view, specify the fit in the field for
S1FIT, S2FIT, etc.
or
In a program, store one of the following constant numbers
or names into a variable S1fit, S2fit, etc.
1 Linear
2 LogFit
3 ExpFit
4 Power
5 QuadFit
6 Cubic
7 Logist
8 ExpFit
9 TrigFit
10 User Defined
Example
Cubic S2fit
or
6 S2fit
Programming