Despite continuing interest in whether plant residues and microwear can give an archaeological 'signature' for the grinding of grain, few studies have looked at what is actually present on ethnographic seed-grinders. In this paper, we map the distribution of use-polish and residues on a classic Central Australian millstone. We begin by setting out an explanatory 'cradle-to-grave' model of the dynamics of millstones to assist our interpretations. We then apply various methods of functional analysis to map the distribution of microwear and residues across the millstone. Several dynamics are evident: (1) the kinetics of grinding create spatial variability in use-polish and residues; (2) systemic factors lead to a palimpsest of different residues, not all of which relate to the major function of the implement; and (3) various systemic factors degrade some of the traces on millstones well before they are buried. Our results for this Central Australian millstone show that there is substantial variability within and between grinding grooves, reflecting the continuing attrition of these surfaces. Starch, which was presumably a primary residue, is poorly preserved, even on the most recent ground surfaces. There is a diversity of other residues present, reflecting secondary use of this millstone as an impromptu work surface. We conclude that the long systemic use-lives of these durable implements can complicate their identification as seed-grinders, and raise issues for future functional research.