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In Germany there are combined thermometer/hygrometer for refrigerators for sale. I placed one of these cheap but surprinsingly good working instruments in almost every room. When humidity changes I put all guitars exept my favourite into their hardshell cases and the cases in the wardrobe. My favourite guitar changes to the room with a better fitting humidity once in a while. The humidity differs in the rooms because of the sunlight oder shadier side side of the room and the possibility to keep the rooms door closed (almost) all the time. If it gets to dry I use a venta humidifier, put all guitars from the wardrobe back on the wallhangers in my homeoffice/guitar romm and my guitars are happy. The venta humidifier is easy to program and very low maintenance. Just change the water once a month and add a liquid. And fill it up in between if needed