Question re humidity sensor controlling 0-10v

I have an air temp/humidity sensor connected to my P4. I have the humidity level determine the 0-10v output (via the IO Box) to an extractor fan that extracts air from above my tank to the outside.

I have set the nominal value of the humidity to 60% with a hysteresis of 3.

I'm having a bit of trouble understanding what determines what voltage is sent to the fan at what level of humidity. So at 61% does it send 1v, 2v, 3v?

And what role does the hysteresis play in this configuration?

The only info I have found in the documentation is:

"The selected controller then outputs a voltage proportional to the control difference (= deviation from setpoint to actual value) on this interface."

Does the hysteresis figure equal full 10v? So at 63% humidity the P4 would output 10v to the fan?

Help? :)