FIG. W-2. Wave definitions. For sinusoids, (a) how displacement at one point varies with time; (b) how wave looks at different places at a given instant. (c) If wavefront approaches at an angle, the apparent wavelength differs from the true wavelength. For nonperiodic waves, (d) dominant period is based on the time between principal adjacent troughs (or peaks); (e) dominant wavelength is measured similarly.