Of a periodic, varying phenomenon, e. G. , an electrical signal or electromagnetic wave, any distinguishable instantaneous state of the phenomenon, referred to a fixed reference or another periodic varying phenomenon. Note 1: Phase, i.e., phase time (frequently abbreviated simply to "phase" in informal usage,) can be specified or expressed by time of occurrence relative to a specified reference. Note 2: The phase of a periodic phenomenon can also be expressed or specified by angular measure, with one period usually encompassing 360&176; (2 radians. ) Note 3: Phase may be represented (a) in polar coordinates by M, where M is the magnitude and is the phase angle, and (b) in Cartesian coordinates, i.e., an Argand diagram, as (a + jb,) where a is a real component and b is an imaginary component such that tan = (b/a,) where is the phase angle, and the magnitude, M, is (a2 + b2) ½ 2. A distinguishable state of a phenomenon. 3. That period of time during which a specified function occurs in a sequential list of functions.