A magnetic field is the magnetic influence of electric  currents and magnetic materials.

           The magnetic field at any given point  is specified by both a direction and a magnitude (or strength); as such  it is a vector field.[nb 1] The term is used for two distinct but  closely related fields denoted by the symbols B and H, where H is  measured in units of amp per meter (symbol: A·m−1 or A/m) in theSI. B is measured in units of tesla (symbol: T)  and newton per meter per ampere (symbol: N·m−1·A−1 or N/(m·A)) in  the SI. B is most commonly defined in terms of the Lorentz force it  exerts on moving electric charges.

           Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments  of elementary particles associated with a fundamental quantum property,  their spin.[1][2] In special relativity, electric and magnetic fields  are two interrelated aspects of a single object, called  the electromagnetic tensor; the split of this tensor into electric and  magnetic fields depends on the relative velocity of the observer and  charge. In quantum physics, the electromagnetic field is quantized and  electromagnetic interactions result from the exchange of photons.

           In everyday life, magnetic fields are most often encountered as an  invisible force created by permanent magnets, which pull on  ferromagnetic materials such as iron, cobalt, or nickel and attract or  repel other magnets.

           Magnetic fields are widely used throughout modern  technology, particularly in electrical engineering and electromechanics. The Earth produces its own magnetic field, which is important in  navigation, and it guards Earth's atmosphere from solar wind. Rotating  magnetic fields are used in both electric motors and generators.  Magnetic forces give information about the charge carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic  circuits.

           Commonly we used the GM500 gaussmeter or teslameter to measure the magnetic strength. and  GM800 fluxmeter to get the flux density of the magnetic.