Aeotec Multi Sensor 6 - best way to check temperature

So I was wondering how other people checked the accuracy of the temperature and humidity readings are the multi sensor 6. I noticed when I switched from USB power to battery power that the temperature deviated quite a bit. But I’m wondering how people figure out what to put for the offset settings.

It’s a known issue/fact that these USB-powered devices run several degrees hotter than battery powered units. I have four on-line at present & use a third-party temperature/humidity readout when calibrating my sensors. And then check that any two placed next to each other for a few days eventually settle on readings pretty close to each other.

All of mine, BTW, are USB powered & have similar calibration offsets.