HP HP-67 - Page 130

126 Simple Programming
Some programs are recorded on both sides of a magnetic card, so the
card must be run through the card reading mechanism twice—once on
each side. If a second side of a magnetic card must be read, the
calculator prompts you by displaying ____|after you have read
the first side. However, the Moon Rocket Lander program is fairly
short, so the complete program has been recorded twice, once on
each side of this factory-prerecorded card. You can easily see when a
card has been read completely because the calculator will then display
the original contents of the X-register. The Moon Rocket Lander
program has now been loaded into the calculator and you can try to
“‘land’’ the calculator on the moon without ‘‘crashing.”’
The Game. The game simulates a
rocket attempting to land on the moon, |
with you as the pilot. As the game be-
gins, you are descending at a velocity of
50 ft/sec from a height of 500 feet.
Velocity and altitude are shown in a
combined display as -50.500, the al-
titude appearing to the right of the
decimal point and the velocity to the
left. The negative sign on the velocity
indicates downward motion. As the game begins, you have 60
units of rocket fuel.
The object of the game is to control your descent by keying in fuel
“‘burns’’ so that when you reach the surface of the moon (altitude 0),
your velocity is also zero and you settle down gently into the powdery
moon dust.
When you press [§, the game begins. The velocity and altitude are
shown in the calculator display. Then the number of remaining fuel
units are shown, and the display begins a countdown to burn time. The
display counts “‘3,”” “2,>” “1,”” ““0.”” When the countdown reaches
zero, you have one second to key in a fuel burn. The best choices for
fuel burns are digits of 1 through 9. A zero burn, which is very
common, is accomplished by doing nothing.
After each burn, the calculator display will show first the new velocity
and altitude, then the remaining fuel units, then will count down to