Analog Hygrometer by Western Humidor

Can this be installed on the outside of a humidor so it reads the humidity inside? I want to dremel out a hole in my humidor and install this.

Many people spoke of recalibrating this unit. How do you know if it needs recalibraing and if it does, how do you know what to set it at?

Can this be used for household humidity or only cigars?

how does it attach to your tank?