A label having an identifier 41L is applied to the upper left corner of the key top of each character key in a left hand region of a keyboard device. The invention furthermore relates to a method for the preparation of air in an aircraft. The housing is provided on a side of the two-stroke gasoline engine and formed with a central part. The contaminant vapor is forced into the heat-conductive pipe through a negative pressure present in the pipe, and transported in the heat-conductive pipe out of the soil.