Each point on the wave completes one period of oscillation in time period T, and we emphasise that all points along the wave oscillate at the same frequency ω. We can consider the term 2π x_0⁄λ in Equation (5.10) as a phase angle. Thus, as illustrated in Figure 5.6, points at x=x_0 andx=x_0+λ, denoted by the open circles, oscillate in phase with each other. As the wave propagates, any particular point on it. for example the wave crest denoted by the bold dots in Figure 5.6, maintains a constant value of transverse displacement y, and hence a constant value of (x-vt). Since (x-vt)=constant, dx/dt=v, which of course is the wave velocity.