How to reliably measure humidity?

Hello,

I am trying to reliably check/measure the humidity in the basement. Meanwhile, I have three hygrometers in use and large differences in the results. For testing, I now have all three standing side by side.

The following values (inside) I have there: 1 (one that measures outside via a sensor, but also inside on the device, company TFA Dostmann): 19.9° temperature, 70% humidity 2 (one that I can also access via an app and via WLAN, it measures directly on the device, company HapopFan) 20.1° temperature, 63% humidity 3 (a very cheap one, available from online retailers in a pack of 3 for 10 euros, also measures directly on the device, sold hundreds of thousands of times, company Thlevel) 20.0° temperature, 55% humidity

Do you have any idea which device is overall reliable (of course, based on the data above you don’t, but I have no problem buying something new, as long as I get a reliable value).

Regards

Do you have any idea which device is overall reliable now

Just take a look at the user manual of the devices. TFA, for example, includes this information with the good devices (e.g. +/-3% between 35 and 75% relative humidity).

Many you also have to calibrate first (wrap in a wet towel for 30 minutes and set to 100%. Have you done that, or is it stated in their instruction manual?

Hello,

thanks already for your feedback.

I will check that, actually I haven't done that. So just unpacked, put in the battery, done.
I will get back to you afterwards.

I have read through the instructions, but unfortunately, there is nothing about calibrating. Does it hurt to try it? Not really, right? Then I will give it a try. Is there a reliable device for measuring, or can you recommend one?

Is there a reliable device for measuring or can you recommend one?

Plenty. Many from TFA are reasonably priced and measure +/-3% or better. But the manufacturer doesn’t really matter.