The present disclosure describes encoding sequence information into a sequence of display frames for display on a display device. Measurements are taken and associated with chosen models giving access to an average temperature of the window, for instance the windscreen, and to a dew temperature of the air in the passenger compartment of the vehicle. The light source is disposed adjacent or substantially adjacent to the light receiving surface, and light from the light source enters the light-guide through the light receiving surface, and is reflected by the light reflecting surface into the first part of the light-guide. The read channel comprises a differentiation circuit for converting the read signal output from the GMR element into the differentiated read signal. Sound attenuating members are mounted in the passageway and a diverter damper is mounted in the housing and is able to direct air flow to either one of the air outlets.