A fuel cell system comprises a fuel cell unit and facility for humidifying process gases to provide a fuel for the fuel cell unit, wherein water-carrying media conduits of the fuel cell unit are provided at least in part as heatable media conduits. The recovery rate for glucose is determined from a non-linear relationship with the recovery rate for the ionic reference substance, and the test value for glucose is corrected therewith. The fuel electrode comprises a plurality of scaffolded electrode bodies. In the folded position, the storage compartment is larger and able to hold more items than when the seat back is in the upright position. The combustor housing is joined to the distributor housing so that the combustion chamber opens into the interior of the distributor. The two-element f-\u03b8 lens corrects the nonlinear relationship between scanned angle and time into the linear relationship between image spot distances and time.