I have three "Cigar Oasis Caliber IV Digital Hygrometer by Western Humidor" hydrometers and I calibrated them using a 65% rh Boveda pack. Then I read a Boveda article and comments that its best to calibrate at 75% to be the most accurate.

So out of curiosity, I purchased the Boveda 75% calibration kit and re-tested all three hydrometers and they were dead on at 75% after 24 hours.

The End.

Ok Rip, now you can go back to sleep.