Re: how to know the trim?
 

The Exducer of the compressor wheel is also called the MAJOR by garrett and turbonetics themselves.

Why they call it "major"?
To avoid confusion with the turbine wheel, on which it's the opposite way around: the small diameter is the EXDUCER and the big diameter is also called major

Re: how to know the trim?
 

As long as you remember:

IN=air in EX=air out

There really shouldn't be any confusion. It's universal to both the turbine and the compressor. It's good to know there is other terminology used in case it comes up though.