When looking for evidence of the golden ratio in works of art, architecture or music, what tolerance should we apply? I argue that the answer depends on what type of object we are testing, how we are measuring, and on a threshold that is not yet known but is introduced here as the Ratio Just Noticeable Difference (RJND). Finally, we describe a variety of experiments that can be used to establish RJNDs for testing evidence of the golden ratio.