Hit Reset to get start the "game". Select returns to the rainbow screen.
Hit Fire to advance levels. The starting number of asteroids will be the first 1-2 digits of score(leading 0 is blanked out). This can be from 4-12.
Every 2 seconds an asteroid will break into two asteroids. This will occur until all the asteroids are small. The middle 2 digits of the score will be how many asteroids are flying around.
Push joystick in any direction to speed things up and break an asteroid every half second.
Last 2 digits of score are flicker level.
0 = no flicker
1 = 30 Hz
2 = 20 Hz
3 = 15 Hz
4 = 12 Hz
Started with 4 asteroids, broken up into 8 asteroids (10 total sprites w/saucer and ship)
Started with 12 asteroids, broken up into 48 asteroids (50 total sprites). Flicker varies from 2 to 4. This is a worse-case sprite count as I doubt it would ever occur during an actual game.
NOTE: these two 2 builds restrict the asteroids to the top 75 and top 100 scan lines to simulate sprite concentration that would occur in Robotron.