ZGC zero gauss chamber reduces the environmental magnetic field (Earth field) to near zero inside the chamber. Any gaussmeter probe which is less than 9.4 mm or 0.370" diameter can be placed inside.
The meter is then "zeroed", which means that it will read zero whenever the probe is subsequently placed in zero field. By using a zero gauss chamber, any offset error is therefore eliminated. The model ZGC is unique in that it contains a degausser (demagnetizer).
This is situated between the inner and outer mu-metal shields. When the degauss button is pressed, any accidental magnetization of the chamber, no matter how strong, is erased. Accidental magnetization is a major problem with most zero gauss chambers and it has limited their use.