HP 39gs Master Manual page 127

The User Defined model
When you set the model to user defined it means that you are expected to supply the complete equation,
including the values of any coefficients. The calculator will not calculate the values of any variables you
include. For example, if you were to supply an equation of
use the values of and
A
could find the best version of the curve for the data.
This may seem to be a useless model but it can be quite useful if you want to experiment with a model that is
not one of those supplied with the calculator.
Connected data
One of the settings on the second page of the
be useful for some types of data. For example, one of the common tasks
in many mathematical courses is the analysis of time series data.
Unlike most bivariate data, time series values are usually plotted as a
line graph - i.e. as connected points. This facilitated by
For example:
The sales of an ice-cream shop are shown as quarterly sales figures for the
years 1992 to 1993. Display this data on a line graph.
Yr
Qtr
1
Sales 12
($1000)
The result (with
Connect
the values in the table were 1, 2, 3, 4, 1, 2, 3, 4 we can't use them
X
that way because it would result in 1992 Qtr 1 being graphed on top of
1993 Qtr 1. The graph on the right was produced by entering values of
1992, 1992.25, 1992.5, 1992.75 etc.
This is not the end of the story though. When you activate
into ascending order based on their x values before graphing. Thus (1,3) (5,4) (2,7) would be graphed as
(1,3) (2,7) (5,4). Not doing this would result in a graph that doubled back on itself and looked like a
scribble instead of a line graph.
currently in memory. By repeatedly adjusting the values of
B
PLOT SETUP
1992
2 3 4
18 20 15
checked) is shown right. Notice that although
as your model then the calculator would
A/(X–B)
screen can
.
Connect
1993
1 2 3
13 20 23
the calculator will always sort the points
Connect
127
and in
A B HOME
4
16
you