This may NOT be the greatest of examples but here is some info on using measurement values in Quark.
001 tell application "QuarkXPress"
002 tell document 1
003 -- My app default is Millimetre Units
004 set a to width of bounds of current page
005 -- Coerce to other Unit
006 set b to (width of bounds of current page) as inch units
007 -- Coerce to other Unit and remove unit identifier for math
008 set c to ((width of bounds of current page) as inch units) as real
009 -- Coerce values to common value for math
010 set d to (("1\"" as point units) as real) + (("25.4 mm" as point units) as real)
011 -- Set any number value to a measurement unit then convert
012 set e to ((d as point units) as inch units)
013 end tell
014 end tell
015 a -- returns "297 mm"
016 b -- returns "11.693\""
017 c -- returns 11.692916870117
018 d -- returns 144.0
019 e -- returns "2\""