I bought a digital hygrometer today (only one I could find). It shows temp and humidity. I followed the directions I found online for calibrating it though I used kosher salt rather than table salt (does that matter?). It has been reading steadily at 68% for the last couple hours. It doesn't have a way to adjust it, so I will just have to calculate for that difference as I go. It has been just over eight hours since I put it in the bag with the salt/water. Is it common for it to be off that much?