original question: In which measurement system [Steradian] is the solid angle unit?
answer: international system of units
answer type: Measurement System.
auxiliary information: The steradian or square radian is the SI unit of solid angle. It is used in three-dimensional space, and functions analogously to the manner in which the radian quantifies planar angles. The name is derived from the Greek stereos for "solid" and the Latin radius for "ray, beam". The steradian, like the radian, is dimensionless, essentially because a solid angle is the ratio between the area subtended and the square of its distance from the vertex: both the numerator and denominator of this ratio have dimension length squared. It is useful, however, to distinguish between dimensionless quantities of a different nature, so in practice the symbol "sr" is used to indicate a solid angle. For example, radiant intensity can be measured in watts per steradian. The steradian was formerly an SI supplementary unit, but this category was abolished from the SI in 1995 and the steradian is now considered an SI derived unit.
What is the measurement system that uses [Steradian] as the unit of solid angle?