A log of transactions is maintained on a persistent storage device. A circuit board, which includes a control circuit, is installed to an axially outer surface of a main body of the rear frame. The diameter of the space section is greater than each diameter of the inlet and the outlet. The conductive layer includes an end portion spaced from the opening, the end portion forming an acute angle with the substantially planar upper surface of the substrate. The power management circuitry or a processor of the biosensor discriminates between intended use and nonuse of the biosensor by the clinician using the sensor signal features.