Radio Shack TRS-80 Operation Manual page 19

Computer Graphics Operation Manual
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However, you'll probably only be able to visually detect a
change in the circle's start and end when PI is accurate
to a few significant digits
(e.g.~.l,
6.28, etc.). The
start and end values can't be more than 2 x PI (e.g.,
6.2832 will not work) or an Illegal Function Call error will
occur.
(~)
Centerpoint
The
(~)
coordinates in the CIRCLE statement specify the
centerpoint of the figure. ~ and yare numeric
expressions in the integer number range.
Example
CIRCLE (~)'I.
CIRCLE (32~,12~),I.
Center
Figure 5. Center of Circle
r
Radius
The radius of a circle is measured in pixels and is a
numeric expression in the integer range. Radius is the
distance from the centerpoint to the edge of the figure.
Although a negative value will be accepted by BASICG, the
results of using a negative value are unpredictable.
The radius is either on the X-axis or Y-axis, depending on
the aspect ratio (see arlo If the aspect ratio is greater
than 1, the radius is measured on the Y-axis. If the aspect
ratio is less than or equal to 1, the radius is measured on
the X-axis.
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