Note 1 to entry: The SI unit of angle is the radian (symbol rad). Other units are the degree (symbol °), the minute (symbol ′) and the second (symbol ″): 1° = (π/180) rad, 1′ = (1/60)°, 1″ = (1/60)′.

Note 2 to entry: The term "plane angle" is only used in place of the term "angle" to distinguish it from the term "solid angle".

Note 3 to entry: The angle between a straight line and a plane and the angle between two planes are defined in IEV 102-04-56 and IEV 102-04-57, respectively.