The expression:
V - 136
computes the numerical deviation above the horizontal axis. The vertical tick marks
are spaced eight graphic cells apart and represent a sales increase
of
50. This means
that each graphic cell is an increase of:
50/8
=6.25
sales units. Thus the expression:
(V - 136)
/6.25
is
the number
of
graphic cells above the horizontal axis. Finally, the Y cell coordinate
is
measured relative to the position
of
the horizontal axis at vertical coordinate 54,
so
the expression:
54 - (V - 136) / 6.25
is
the vertical cell coordinate. For example, the first quarter sales is Y = 160. The
vertical coordinate
is:
54 - (160 - 136) / 6.25 = 54 - 3.84 = 50.16
which rounds to 50. The first quarter sales point
is
therefore graphic cell
(39,50).
Line 779 This NEXT statement terminates the FOR loop begun in Line 750.
Lines 988 - 958 These Data statements contain the six years
of
sales values in
chronological order.
Line 2888 This endless loop prevents termination
of
execution
so
that the cursor does
not interfere with the graph.
Experiment
#7
Connect the Points
The readability of the graph created in the last experiment can be improved
by
connecting the data points with straight lines. This
is
rather easy on the Model 100
using the LINE statement.
Add the new line:
745 PSET (39,50)
and
change line 760 (this is easy with the Editor)
to
760 LINE - (33 +X*6,54- (V
-136)/6.25)
List the program to confirm that it is:
50
100
150
200
300
500
CLS
LINE
<239,5£1)
LINE
-
(33,O)
FOR
}{
=
33
TO
PSET
(}{
,53)
FOR
'{
=
51
TO
-
(33,5£1)
239
STEP
2£1
NEXT
X
°
STEP
-8
107
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