Abstract: Tire pressure indicator having a wheel mounted transponder unit and a hand-held interrogator unit which can be positioned for coupling with the transponder unit. The transponder unit is a passive device which returns signals to the interrogator unit in accordance with the pressure in the tire mounted on the wheel. When the tire pressure is above a predetermined safe level, a "safe" light on the interrogator unit is illuminated, and when the pressure is below the safe level, a "low" light is illuminated. Operating power for the interrogator unit is supplied by a battery in the unit, and the lights are flashed at a visible rate when the battery voltage drops below a predetermined level.

Abstract: System for sampling and holding an analog signal corresponding to the altitude of an aircraft and providing a control signal for maintaining the aircraft at the altitude where sampling occurs. A binary converter stores a count corresponding to the level of the sampled signal, and a digital-to-analog counter provides an output analog signal corresponding to the count registered by the counter. The altitude signal is compared with the output signal to provide an altitude correction signal in the event that the altitude signal deviates from the level corresponding to the stored count.