HP 39g Master Manual page 168

The operation of the two modes is summarized below.
PLOT
mode
The underlying concept in PLOT mode is
that the graph controls the equation.
The user has control of the graph via two manipulation points (see above and
below) and any changes to the graph are reflected in the equation at the top
of the screen.
Looking at the screens on the right it will
be seen that the third screen key toggles
the point of control for the graph. It is only
visible in PLOT mode.
When in PLOT mode the graph is changed using the arrow keys. The effects
of the arrow keys vary according to the location of the control point.
• when control is set to
translates left and right (the c coefficient) or
up & down (the d coefficient).
• when control is set to
dilates parallel to the y axis (the a
coefficient) or parallel to the x axis (the b
coefficient).
Unlike the SYMB mode where the b coefficient goes up or down in steps of
0.1, the increments in PLOT mode are not regular but are chosen to be 'nice'
π
fractions of . The slight difference in results is most easily seen by simply
experimenting.
SYMB
mode
The underlying concept in SYMB mode is that the equation controls the graph.
The user has control of the coefficients and any changes are reflected in the
graph.
All four coefficients are shown at the top of the
screen even when one or more is redundant.
the graph
the graph
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