They read up to 1 bar negative(vacuum) and up to 2 bar positive where as the std one just does 1 bar positive, 1 bar negative.
This bit about 1 bar atmospheric is wrong, atmos is atmos but it is reading DEPRESSION(NOT ATMOSPHERIC) VACUUM, or negative pressure, when NOT on BOOST, ie VACUUM, it changes to POSITIVE READING WHEN ON BOOST.
tabetha