B737Ng rudder trim is measured in UNITS of TRIM,up to 16 units left,zero units(neutral),or up to 16 units of right trim.
I can`t speak for some NG aircraft that use flight control position information as displayed on the lower Display Unit as that OPTION is not in use on the aircraft i maintain.
It can be referred to in inches of travel whilst carrying out rigging of the rudder as per the manuals.
Regards DDG