Conversions can be done either with the "->" conversion operator or with the equivalent "convert" function. The function has three parameters: a quantity, a unit to convert from and a unit to convert to. Likewise the conversion operator uses three values: the quantity and unit to convert from are placed on the left side of the operator while the unit to convert to goes to the right side.
The basic unit of solid angle is the steradian. All units of solid angle are expressed in terms of this base unit and so measurements can be converted from any one of the following units to any other.
2 pi steradian -> spheres = 0.5
convert(2 pi; sterad; sphere) = 0.5
1/4 sphere -> steradian = 3.1415927
convert(1/4; sphere; sterad) = 3.1415927