Try doing to salt test. You'll find it everywhere on the internet. Then if the hygrometer is wrong, you'll know how off it is. Does your thermometer have a probe? Inside means the area around the thermostat and outdoor means the area where the probe is. If you have the whole unit under the bedding, I would remove it and just let it prop against the wall of the tub. Remember, thermometers (excluding temp guns and probed thermometers) measure ambient/air temp so you'll want it where the air is. If there is a probe, just place it on the surface if the bedding on the opposite side of the cage.
0.1 Super pastel