This is a "How-To" on "Decathlon". But if you came here for information on how to train for a Decathlon, I'm afraid you're going to be disappointed!!
I had Decathlon for my Atari 400 (and Atari 800XL and Atari 130XE) computers. And as others have mentioned, it was a great game that you just kept coming back for more, just to try and score one more point in each event!
I was a member of an electronics club in my school (yes, I'm a geek). We learned the basics of electronic components and "building block" circuitry. Including multivibrators.
I was a subscriber to Atari User magazine. This was for a number of years the only mainstream magazine in the UK dedicated to the Atari 8-bit computer range. On occasion, it would run a "series" of articles in consecutive magazines. And one of these was about controlling external hardware devices from your Atari computer - which was pretty simple because the joystick ports could easily be changed into output ports, giving you 8 on/off control lines. But as part of this, they had published the pinout for the joystick port.
Benjy the cheating geek
So, you can probably see where this is going.
I built an astable multivibrator using the components from my electronics club. I then, using a joystick extension cable, connected it across the "left" and "right" pins of the joystick input. All I then needed to do was play with the resistors and capacitors in the circuit (which determine the period of the astable) until they sent pulses into the computer at the optimum rate for Decathlon to think I was running as fast as is possible! It also had a switch to connect the pins through to the joystick, so I could play other games!
Somewhat like an "autofire" button on a joystick - but for running!
Needless to say I set some amazing scores with this. I think at one point, I managed to score over 1000 in every event, although unfortunately I have no pictures or record of this. Of course, while it made the 3 straight running events (100m, 400m and 1500m) no-brainers, there was still an element of skill in the throwing and jumping events as your timing was crucial as well.
Did I ever use this to cheat against friends? I couldn't possibly say!