I have been practicing with palm and have been getting inconsistant results. From what I know there should be approx 1 difference (depending on how or dark your skin is) between your palm and a greycard. I have found this to be mostly true but have also had a varitey of results from 1/3 of a , 3/4 of a , 1 1/2 and EVEN no difference between my palm and greycard!!!... a little confused. Anyone out there shed some on the matter?