Abstract: An altimeter (24) of the aneroid type having a correctable digitizer 26 is shown. When the pilot sets the altimeter to the local barometric pressure, the correctable digitizer is also set to the local barometric pressure. An input device (58) connected between the barometric pressure correction control (66) and the digitizer (62) generates a barometric pressure correction signal (67) which is routed to digitizer (62). Barometric pressure correction signal (67) modifies the aircraft altitude output value of digitizer (62) to a corrected aircraft altitude output value (68) which is routed to one or more external navigation systems (70).

Abstract: An optical grating having expansion characteristics equivalent to the thermal expansion characteristics of a preselected material is formed by providing a thin grating sheet of a material different from the preselected material, forming spaced slits in the sheet to overly an opening in an underlying plate of such preselected material, thereafter securing the sheet to the plate along narrow zones outside the opening, and finally removing the portions of the sheet lying outside such zones.

Abstract: An inexpensive, compact and yet highly accurate instrument for transmitting coded signals representing altitudes at which an aircraft is flying, the instrument comprising an altitude sensing unit and a separate encoding unit operatively connected to the sensing unit with means for finely and precisely adjusting the encoding unit relative to the altitude sensing unit.