The nature of the angle measure we are dealing with is determined, strictly speaking, not by the angle, but by the function, but the two types of function (that might be separately denoted by, say, degree-sin(x) and radian-sin(x)) are, for the sake of convenience, conflated, and therefore we have to resort to a voice-over to indicate which angle-measure is being employed. Typically, angles in degree-measure are expressed as raw decimal real numbers, whereas angles in radian-measure are expressed in terms of something involving pi (coinciding, of course, at the special value 0), however this is mere convention, not strictly a mathematical rule or result. For example, radian-cos(pi) = -1, but degree-cos(pi) is approximately 1.