153??? I echo that jaw dropper.
Why is it unofficial if its ATP not Davis Cup?
As long as there's a gun there, and its an official match, its official I'd imagine.
I would think with the dimensions, there would have to be some
sort of threshhold. Unless some guy 7-foot was serving!
The possibilities have a lot to do with the racquet technology.
I haven't seen a Guiness Book of World Records in quite some time, but last I saw, they listed Bill Tilden with the fastest serve ever at 163.6 mph. I think they measured that one with a sun dial!