How can I plot the ratio of input 1 and input 2?

By default, each channel shows the ratio of the input to the output, In / Out. This is useful for measuring the transfer function of a device under test. The math channel allows you to plot different combinations of Ch 1 and Ch 2. If the output amplitudes of both channels are set to the same value, then viewing the math channel as Ch 1 / Ch 2 will show the ratio In 1 / In 2, since the outputs are the same.