I believe The Match unit is label the 0-9 unit. bottom right with bell.
http://ipdb.org/showpic.pl?id=2288&picno=66171&zoom=1
I was having an issue on a bally and I had to clean the 1st score reel. (the lowest scoring reel). On my bally the match value changed each time the 1st score reels rotated. (Except during game reset). The match value is compared to the 1st score reel. If they match, a credit is awarded.