We present the first linear relationship that explains both the rotation curves of disk galaxies and the dynamical masses of galaxy clusters, without the need for any dark matter. A previous paper analysed the rotation curves of galaxies from the SPARC catalogue and a linear relationship was found. Similar analysis has been applied to recently published data on galaxy clusters and the same linear relationship has been found. This linear relationship is an observational result, not a theoretical one. It rules out the requirement for any dark matter in disk galaxies and galaxy clusters.Given the distribution of baryonic matter (stars, gas) in a spiral galaxy, we can use the linear relationship to predict the rotation curve; something dark matter cannot do. And given the distribution of baryonic matter (gas, galaxies) in a galaxy cluster, we can use the same linear relationship to predict the dynamical mass; again, something dark matter cannot do. The analysis is interpreted as meaning the energy scale varies from location to location. No dark matter is required, and no changes to Newtonian gravitation are required either; just a simple variation of the energy scale.