Ya analogue unfortunately
Go get a digital, use the salt method to calibrate it, and then see where the rh is falling. If you use heartfelt beads or kittly litter you can almost rest assured your going to be right on the nose.
The salt method consists of placing some salt in an open container, anything from a coke lid to a small bowl and then adding enough distilled water to make it wet, not soupy, just wet. You don't want to see water standing on top of the salt but you don't want dry salt on top. Place the hygrometer in the baggie or airtight container with the salt mixture and in 24 hours, no matter what the hygrometer says, the rh is 75. Most analog come with a button you can press that sets them to 75, that's why the baggie works well here.