A new tool has been developed to help elucidate the differences in packing between different polymorphs, especially when the differences of interest are small. The technique builds upon the Hirshfeld fingerprint plot pioneered by Spackman and co-workers by subtracting the value at every point in a fingerprint plot from the value at every point in another. This is found to reveal differences that are not readily apparent to the eye. By summing the absolute values of these differences, a quantitative measure of the difference between two fingerprint plots can be obtained. The technique was applied to Ni and Cu trans-bis(2-hydroxy-5-methylphenonethanoneoximato) complexes determined at two temperatures, with the Ni complex displaying temperature-dependent polymorphism. Difference Hirshfeld fingerprint plots were also generated for calculated structures from DFT simulations that were performed on the experimental structures. These demonstrated that the simulations reproduced the fine detail of the packing.