<p>We present a novel challenge to Inheritance – roughly, the thesis that the phenomenal character of an experience is determined by the external things that the subject experiences. The challenge is based on Weber’s Law, an old and well-established psychophysical finding. The challenge is novel, first, because it undermines Inheritance indirectly, by focusing on an independently interesting, related thesis about how phenomenal <i>dissimilarities</i> are determined; second, because it only minimally appeals to introspective judgments; and third, because the standard response to earlier challenges, which is to propose “alternative” properties that our experiences are of, is ineffective against it. Along the way we discuss interesting questions about the nature of physical length, measurement theory, and the metaphysics of dissimilarities.</p>