The term "phase" is also used when comparing a periodic function F with a shifted version G of it. If the shift in t is expressed as a fraction of the period, and then scaled to an angle φ φ spanning a whole turn, one gets the phase shift, phase offset, or phase difference of G relative to F . If F is a "canonical" function for a class of signals, like sin ⁡ ⁡ ( t ) is for all sinusoidal signals, then φ φ is called the initial phase of G .