To monitor a concentration of an analyte in a human or animal body in vivo, and measure the course of changes at time intervals, values are measured at time intervals by a sensor (1) with a wireless link to a receiver (2), which is linked to an evaluation unit (3) incorporating a microprocessor (4) and a data store memory (5). Data and commands can be set at the evaluation unit from an input (6). The results are shown on a display (7). To forecast an analyte value over a forecast time period, a function is determined according to the analyte values with the time course of the analyte value in the vicinity of the time point, with a given accuracy or approximation.
