I recently posted a thread, 'who to believe' about the 3 hygrometers I have and how differant their reading were. I did some research after reading the post from poolboy101 about using a salt solution to calibrate them (I think he had the amounts backward). Anyway, I ran across this site on using the salt method to calibrate them. It also included a table of many other chemicals one can use for calibrating at lower humidity levels and is extreemly informitive.

oh yes, if anyone has Magnesium Chloride Hexahydrate, or knows where to get it locally, I love to try the 33% calibration.