This Electro-Magnetic Field tester is designed to provide the user a quick, reliable and easy way to measure electromagnetic field radiation levels around power lines, home appliances, computer monitors, TV sets, video machinery, industrial devices and other similar devices.
The following information is provided by NRPB of UK and hopefully this is helpful:
(Distance ) 3cm 1meter
Microwave 750 ~ 2000mG 2.5 ~ 6mG
1 Tesla = 10000Gauss
1Gauss = 1000mG