Accurate way to measure humidity

[curdogs]

I have a acu-rite that has humidity and temp, and a coil spring type that reads 65% and the acu-rite reads 33%.
What do you all trust

 

[silkiechicken]

I use the wet bulb/dry bulb method... but I do not measure it for hatching eggs, just watch air cell growth plus trial and error.

That said, there is a saturated salt water method of seeing how far off your hydrometer is, so you can compensate for it. I don't know this method myself beyond making a saturated salt slurry in a bag, and putting hydrometer in said sealed bag, for which it should read 50%. But that is what my faint memory says.