I have been using Boveda packs for 5 years now and have had no problems.  I bought a Boveda calibration kit a while ago, and I just use the Boveda Salter HygroSet II and read it with a digital hygrometer. I also just got a cheap (less than $2)  digital  hygrometer/thermometer to have in the box, but have never calibrated it.  I have never used a humidifier, and have never had a problem with my cigars.  Some of my cigars are over 10 years old.  I live in Tucson and the humidity in the summer gets up to 50% for a few weeks.  The Boveda packs keep my cigars perfect.  Another thing I like about Boveda is that if one of them fails in the humidor, it won’t ruin all my cigars, as it has a very slow leak. Now you can check more reviews about Cigar Hygrometers click here https://smokeprofy.com/reviews/best-cigar-hygrometers/