Spidertronic
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Get a high score and enter 'CHEAT', press return followed by the fire button.
The screen will go black; a prompt will appear: "Last game level: GAME.LS0". 
Now type 'GAME.LSx' and the number of the level you want to play instead of
"x". Press return, followed  by the fire button, and you start playing on the 
desired level.