use a ruler and measure the length of how many wavelengths have passed on the piece of paper by taking a picture on the phone so the wavelengths are static
divide the length of the total wavelengths by how many waves to get 1 wavelength
how to find the frequency
see how many waves go past in a set amount of time (e.g 10 seconds)
divide the total amount of waves by the time period to get the frequency
