Just an additional note, more beads are better than too few. I have a 600 ct humidor and had been getting by with about .75 lbs of beads, had to add a damp sponge about every week. The beads were in a bowl. Then I bought some of the flat humidification sheets from viper for my travel humidor (no spillage problem and flat) and bought an additional pound of beads. I put these in the mesh bags ( someone suggested getting the bags for rice or birdseed for weddings and made up about 10 bags (2" diameter) and placed them around the humidor. I put a damp sponge in and went on 3 week vacation, still the same humidity when I returned and today I will have to dampen the sponge again as the humidity has dropped to 67 from 70%. This is after 5 weeks.
This just confirms at least in my mind, what others have mentioned about extra beads providing a safety buffer and will equalize the humidity for longer periods.