Humidity sensors problem(?)

I bought 3 ruuvitags couple of weeks ago and I’ve done the salt test a few times. First time I got around 62H% but I thought I messed up the ratio of salt and water.

I took them out, let them level out and they dropped to around 39%. After this I did another test and this time I got to 66-67%. At this time I took one of the ruuvitags out from the bag and placed it in a container with another humidity tester and salt mixture. The other humidity tester shows 73%, as expected with a little offset but the ruuvitag only shows 66%. I’ve let them marinate for few days and the RH% has not changed a bit on either devices.

This is how the container looks, bit of a bad pic due to scratches on the plastic

Both calibration containers

Am I doing something wrong or is there a problem with the sensors? Are there another tests I can perform etc.? I am going to use these on a remote location through raspi so I need know they are precise.


Some information about this can be found at,-humidity-accuracy