Radio Shack TRS-80 Operation Manual page 26

Video Centering Test
Type in the following to insure your television display is centered
correctly on the screen.
NEW
10 CLS (ENTER)
15 FOR X = @ TO 63 (ENTER)
20 Y = 15 (ENTER)
25 RESET (X,Y) (ENTER)
30 NEXT X (ENTER)
35 FOR Y = @ TO 31 (ENTER)
40 X = 31 (ENTER)
45 RESET (X,Y) (ENTER)
50 NEXT Y (ENTER)
55 GOTO 55 (ENTER)
To check for typing errors, type:
LIST (ENTER
It should look like this:
10 CLS
15 FOR X = @ TO 63
20 Y = 15
25 RESET(X+Y)
30 NEXT X
35 FOR Y = @ TO 31
40 X = 31
45 RESET(X+¥)
5@ NEXT ¥
55 GOTO 55
If you find an error, simply re-type the line.
Next type:
RUN
You should have a green background, surrounded by black, with a
horizontal and vertical line (both black) intersecting in the exact
center of the screen.
You can now adjust your set until the display is centered.
Press (BREAK) to stop the program.
Notes on Video Centering
The COLOR COMPUTER generates a rectangular image designed
to fill most of your TV's screen. Use the horizontal- and
vertical-centering controls on your TV set to center this image as
much as possible.
Don't worry if you can't get a perfectly centered image, or if you
notice a slight distortion in certain areas of your TV screen. These
minor variations depend on the condition of your TV set. (If they
are severe, you should consult a qualified TV service technician.)
Sound Demonstration
The following program will output the entire frequency range
(codes 0-255) COLOR BASIC can produce.
NEW (ENTER)
10 FOR X = 1 TO 255 (ENTER)
20 SOUND X,1 (ENTER)
30 NEXT X (ENTER)
To check for typing errors, type:
LiST (ENTER)
It should look like this:
1@ FOR X = 1 TO 255
2@ SOUND X» 1
30 NEXT X
If you find any errors, simply re-type the line.
Set your television volume to a normal level, and type:
RUN (ENTER)