newbe turbo kit question

[JPG0511]

i have decided to go with a turbo kit for my s13 and i have a question. i am looking at the stage one kit from boostdesigines. i want to start with a cheep low boost set up since this is my first turbo install. they list this part in the list FMU w/ 12:1 Disc . and i was wondering what that is? thanks for any help you can give. sorry i found it in another post. thanks anyway