Here's another. Imagine you want the ratio of two clock sources. Put them both through frequency dividers, with one divider output put through a phase shifter.

Here's another. Imagine you want the ratio of two clock sources. Put them both through frequency dividers, with one divider output put through a phase shifter. compare the resultant divided frequencies by xoring the signals together. The ratio of the frequencies is given by the ratio of the dividers when you can find a phase shift such that the xor output doesn't change. The time you wait to see if the xor output doesn't change represents the certainty you have in your ratio. This is called the time frequency uncertainty relation, also known as the Heisenberg uncertainty principle.