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Finding Period and Frequency

You can measure the period from the history graph: it is the time between two successive crests, troughs, or other matching parts on the wave. Alternatively, you can count the number of cycles $N$ that occur during a certain time $t$, and then $T=t/N$.

If you are given a snapshot graph and the wavespeed, you can measure the wavelength from the snapshot graph, and then use the formula $v=\frac{\lambda }{T}$.