I measured ELF in my work place, one of the rooms has highest, 10-20mG on floor, as the probe goes away from the floor, it decreases, finally at the face height, it's 2mG.
The next room of this affected room has AC unit and downstairs has big transformer for electricity.
I guess it's coming from the downstairs garage.
Is there any way to block EMF coming from the downstairs? Maybe putting some kind of shielding on the ceiling at the downstairs?