By committing to and following the ABC Dry Cleaning business system to a tee, he has taken this small struggling store, from $86,000 to a whopping $552,941.00in 2008. This is from an advertisement of a dry cleaner. I'd like to know the meaning of "follow something to a tee". It seems to be an idiom but I have no idea what it means. What does "tee" mean here?