The international system for units.
Le Systeme international d'Unites officially came into being in October 1960 and has been adopted by nearly all countries, though the amount of actual usage varies considerably.
It is based upon 7 principal units:
Length - metre(m)
Mass - kilogram(kg)
Time - second(s)
Electric current - ampere(A)
Temperature - kelvin(K)
Amount of substance - mole(mol)
Luminous intensity - candela(cd)
From these basic units many other units are derived and named.

(T) The SI unit of magnetic flux density.
Definition: 1 T is the field intensity generating 1 newton of force per ampere of current per meter of conductor. The tesla unit value is defined as a field strength of 1 weber per square meter of area, where 1 weber represents 1 x 108 (100 000 000) flux lines.
One T is equal to 10 000 gauss, the older (CGS) unit. A field of 1 tesla is quite strong, the Earth's magnetic flux density, at its surface, is about 50 microteslas (μT). The slew rate of MRI devices is measured in mT/m/msec or T/m/sec.

(W) The SI unit of power.
Definition: 1 watt is equal to a power rate of one joule of work per second of time or in electrical terms it is the power produced by a current of one ampere flowing through an electric potential of one volt.
Power is the rate at which work is done, or the rate at which energy is expended and is used both in mechanics and in electricity.
The unit is named for James Watt, a British engineer.