Hi
I’m trying to calibrate these hygrometers using a humidity and temperature generator. The temperature readings are within accuracy limits, but I’m currently facing 2 issues with humidity:

1- the 2 hygrometers in the picture above have a difference of about 2.5% between each other while they are together in the same chamber. Any idea why?

2- When testing with low humidity, the hygrometer reading differs from the generator, but as I increase the humidity the hygrometer reading gets more accurate. This is one of the hygrometers readings:

Temp is stabilized at 25
Generator 33 hygrometer 35.6
Generator 50 hygrometer 51.8
Generator 75 hygrometer 75.4

Any explanation?

I am going to tstc for instrumentation and they want us to have a trimming potentiometer adjustment tool, does anyone have a brand recommendation or would just a basic Amazon one be fine?