Grav Documentation
-------------------

By David F. Kurth

This is my first attempt at writing anything substantial for the
HP48 calculator.  I wrote this in PASCAL about 10 years ago for
a HP3000 computer, then rewrote it in BASIC for a primative home
computer, and then massaged it into this for a great handheld calculator.
I am not a programmer, but enjoy trying to get something to work
the way I want.  This program is by no means perfect, but I enjoy
playing it and wanted to share with everyone else.
Have fun playing.

Dave Kurth

GRAVITY GAME

Original Concept Stolen From Some Ancient HP Desktop Calculator

Written for HP48 by Dave Kurth  06Jun91  Ver 1.0

Object:  Launch a missile from your station (a cross or X
on the left side of the screen) to hit a target (a bull's-eye
on the right side of the screen).  Two to five planets affect
the missile's path due to their gravitational field.  Larger 
diameter planets have more influence.

Controls: Your only input is the firing angle of your missile.
An angle of 0 degrees shoots horizontal to the right.  90 degrees
is straight up.  If there is too much planet mass behind your
station, you may not be able to reach the target.  On the other
hand, an indirect missile path may have surprising results.
Be careful, or you may hit yourself!  Your station and the target
have no gravity, so they will not "attract" the missile.

Caution: This game is realtime.  One must realize that when using
convention missiles without warp drive travelling way below the 
speed of light, it takes time to cover such astronomical distances.
This game is ideal for long boring meetings where you have time 
to burn and want everyone to think you're still solving those 
complicated problems that *required* the purchase of your calculator 
in the first place.

Starting: Download the program to the calculator,
then push the GRAV menu key to start the program.

For a simple demo, enter "2" for a seed and 10 degrees for the angle.
This direct shot takes about 30 seconds.
For a crazy demo, enter "2" for a seed and 20 degrees for the angle.
Now wait about 7 minutes and see what a different path the missile
follows to hit the target.  When the missile is travelling, any
keystroke (other than ATTN/ON) will abort the current shot.  You 
may abort because you think your shot will miss.  If you let the 
missile continue though, you may find the missile will go around 
again and eventually hit the target.  This is what makes the game
fun to watch and predict.

This is presented with no rights reserved.  I take no responsibility
for any damage or injury to anyone caused by this program.  I
believe the physics are correct, but then again all the constants
are made up to fit the "universe" on the screen.
I'm no expert on the HP48 (I've only had one since Feb).  I only
wish things would go faster.
  
Above all, have fun and maybe you'll learn something new.
