CRP5 IS SHORT FOR CRAP 5. JUST DONE THE JAA EXAMS MYSELF ANSWERS ARE NOT VERY ACCURATE WHEN USING THE '5' SO WE WERE TOLD TO JUST TO USE ISA DEVIATION MULTIPLYED BY 120.
FOR TRUE ALT CALCS TRY USING ISA DEVIATION MULTIPLY BY 4 {CONSTANT) THEN MULTIPLY BY HEIGHT IN THOUSANDS.
E.G -5 MULTIPLY BY 4 MULTIPLY BY 12(12000)
GIVES A MUCH MORE ACCURATE ANSWER AND ALL OUR CHAPS ARE PASSING NAV SO GIVE IT A GO.