An aromatic polyanhydride comprising a repeating unit having the structureis disclosed, wherein Ar and R are selected so that the aromatic polyanhydride hydrolyzes to form a therapeutic salicylate, another non-steroidal anti-inflammatory, an antifibrotic aminobenzoate, or a vasoconstricting phenylethanolamine. The counter comprises an array of cells, wherein each cell is configured to hold a digit in a redundant base-k representation of a number contained in the array of cells. A face plate is fixed to the mounting shaft proximate the motor housing and cooperates with a clamping assembly to sandwich and dynamically center the vehicle wheel on the shaft.