The score reel circuit boards are used when the game needs to know more about the score. Most score reels have switches to distinguish 0 and 9 from the other positions which is enough to handle the carry (9->10) and resetting functions. But there are two other functions that need more information: match and high score. These functions need to know which position the score reel is in so a circuit board is added to distinguish between all 10 positions.
Egg Head replay (resized).jpg
I don't have a Cross Town schematic handy, but on Egg Head for example the 1s and 100s score reels are used for match and high score functions to add a replay.
/Mark
