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The fundamental constants of nature, as presented by modern science, can be conceived as natural measures of the universe. In comparison, the standards of the International System of Units, including the kilogram and the meter, are mind-made and hand-crafted to meet the demands of human life. In this paper, the gap between the natural and the conventional is squeezed from two directions. In the first place, we come to understand why the metric measures were originally conceived, by the best of scientists, as being “taken from nature” and “in no way arbitrary”. The kilogram of yesteryear was anchored in yesteryear's science and is reasonably considered natural with respect to that science. We also review a contemporary debate amongst physicists that questions whether any quantity, being necessarily written with units, can be truly fundamental. Modern notions of a fundamental constant are put under the spotlight; the kilogram emerges as bound up with contemporary science today as ever it was. In the picture being painted here, our measures are drawn as dynamic entities, epistemic tools that develop hand-in-hand with the rest of science, and whose significance goes much further than a metal artefact dangled from an abstract number line.