Measuring water waves in a ripple tank

Frequency of a wave can be measured indirectly from its speed and wavelength. Wavelength of a wave can be measured by using a freeze frame of a wave moving along the length of a ruler. It is more accurate to measure the length of, e.g. ten waves and dividing by ten, than measuring one wavelength. Speed of a wave can be measured by recording the wave moving along a ruler with a timer in the frame. Accurate distance and time are measured by freezing the film, played back in slow motion, to track one wave crest.