I heve observed as on the picetures on two A3 devices in two rooms next to each other.
Devices are new (bought about year ago but just started couple of days ago). Why such difference?? Is it normal to have Formaldehyde result difference between devices so big?
I’d say yes, this is possible. A year is a lot and there can be some drift, regardless of the devices being energised or not. Get them running together and let me know here or via supoort email to check the calibration parameters for the two. Some adjustments are possible.