salt test question

I put new battwries in my hygro so I needed to recalibrate. I put it in a baggie with a pop cap full of wet salt. Not watery just a grainy, salty, slurry. After 6 hrs I read 76%, after 12 still 76%, It read 76% up until about 34 hours into it when it went to 72% and there it sits 48 hours later at 72%. My instructions for the Hygroset say test 24-36 hours, which do you think is a more accurate representation the 76% or 72%.