Carl Friederich Gauss (1777-1855) is considered one of the greatest mathematicians who ever lived, and he was also a pioneer in the study of magnetic fields. He developed one of the first devices capable of measuring the strength and direction of a magnetic field, the magnometer, and he also developed a system of units to measure magnetism. In his honor, the modern unit of magnetic flux density or magnetic induction in the CGS (metric) system is named the gauss. In the more inclusive SI measurement system, the basic unit of magnetic flux is the tesla (named after Nikola Tesla). One tesla equals 10,000 gauss.

A gauss meter is a modern version of Gauss' magnometer. It consists of a gauss probe, the meter itself and a cable to connect them, and it works because of the Hall effect, which was discovered by Edwin Hall in 1879. It can measure both the intensity and direction of a magnetic field. You use a gauss meter to measure relatively small magnetic fields. When you need to measure large ones, you use a tesla meter, which is basically the same thing, but graduated in the larger tesla units.

Electricity and magnetism are related phenomena, and a magnetic field can affect an electric current. If a current is passing through a conductor, and you place the conductor in a transverse magnetic field, the force of the field will push the electrons to one side of the conductor. This asymmetric concentration of electrons creates a measurable voltage across the conductor that is directly proportional to the strength of the field (B) and the current (I) and inversely proportional to the charge density (n) and the thickness of the conductor (d). The mathematical relationship is:

V = IB/ned

where e is the charge of a single electron.

The gauss sensor is basically a Hall probe, and it's the most important part of a gauss meter. It can be flat, which is best for measuring transverse magnetic fields, or it can be axial, which best measures fields parallel to the probe, such as those that exist inside a solenoid. Probes can be fragile, especially when designed to measure small fields, and they are often fortified with brass to protect them from harsh environments.

The meter sends a test current through the probe, and the Hall effect produces a voltage which the meter then records. Magnetic fields are seldom static, and because the voltage fluctuates, the meter usually has features that freeze the reading at a particular value, capture readings and save them, and record only the highest voltage detected. Some meters distinguish between DC and AC fields and automatically calculate the root mean square (RMS) of AC fields.

Gauss meters are useful devices, and an electrician who has one can diagnose miswired circuits more easily. In fact, a non-contact voltage tester detects electricity flow by the magnetic field it produces, so it is a type of gauss meter. You can use a gauss meter to measure the strength of the magnetic field around power lines, although technically you would need a tesla meter because of the strength of the field. You can also use a gauss meter to measure the strength of the ambient magnetic field in your house. This field changes according to which appliances you use.

While the effects of magnetic fields on health are not established, there is some evidence that prolonged exposure to high magnetic fields can be harmful. If you're concerned about this, you need gauss measurement tools. A gauss meter gives you the capability to regulate the field strength in your house.