Usually, whole turns are ignored when expressing the phase; so that φ φ ( t ) is also a periodic function, with the same period as F , that repeatedly scans the same range of angles as t goes through each period. Then, F is said to be "at the same phase" at two argument values t 1 and t 2 (that is, φ φ ( t 1 ) = φ φ ( t 2 ) ) if the difference between them is a whole number of periods.