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According to ISO 764 or its equivalent DIN 8309 (Deutsches Institut für Normung - German Institute for Standardization) a watch must resist exposure to a direct current magnetic field of 4800 A/m. The watch must keep its accuracy to ±30 seconds/day as measured before the test in order to be acknowledged as a magnetic-resistant watch.
The gauss is the unit of magnetic flux density B in the system of Gaussian units and is equal to Mx/cm 2 or g/Bi/s 2, while the oersted is the unit of H-field. One tesla (T) corresponds to 10 4 gauss, and one ampere (A) per metre corresponds to 4π × 10 −3 oersted.
One difference between the Gaussian and SI systems is in the factor 4π in various formulas that relate the quantities that they define. With SI electromagnetic units, called rationalized, [3] [4] Maxwell's equations have no explicit factors of 4π in the formulae, whereas the inverse-square force laws – Coulomb's law and the Biot–Savart law – do have a factor of 4π attached to the r 2.
In the CGS system, the unit of the H-field is the oersted and the unit of the B-field is the gauss. In the SI system, the unit ampere per meter (A/m), which is equivalent to newton per weber, is used for the H-field and the unit of tesla is used for the B-field. [3]
This page lists examples of magnetic induction B in teslas and gauss produced by various sources, grouped by orders of magnitude.. The magnetic flux density does not measure how strong a magnetic field is, but only how strong the magnetic flux is in a given point or at a given distance (usually right above the magnet's surface).
In SI units, permeability is measured in henries per meter (H/m), or equivalently in newtons per ampere squared (N/A 2). The permeability constant μ 0 , also known as the magnetic constant or the permeability of free space, is the proportionality between magnetic induction and magnetizing force when forming a magnetic field in a classical vacuum .
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1 maxwell = 1 gauss × 2. That is, one maxwell is the total flux across a surface of one square centimetre perpendicular to a magnetic field of strength one gauss. The weber is the related SI unit of magnetic flux, which was defined in 1946. [9] 1 maxwell ≘ 10 −4 tesla × (10 −2 metre) 2 = 10 −8 weber