Abstract: A pressure transducer cross-check system (10) in which a pair of low precision pressure transducers (12, 14) which detect parameters related to each other in content are alternately periodically calibrated during the operation of the system by cross-checking by a solenoid actuated valve (18) which alternately connects one of the pair of low precision pressure transducers (12, 14) to its associated pressure input (20, 22) while connecting a common high precision pressure transducer (16) to the other of the related pressure parameter inputs (20, 22) for selectively alternately providing one of the pair of parameter input signals as a high precision pressure responsive input signal to the system controller on alternate cycles of the low precision pressure transducer pair in accordance with the cycling of the valve (18).

Abstract: A mach airspeed indicator capable of internally determining mach number and VMO from measured altitude and airspeed information directly. An internal microprocessor, capable of storing a plurality of selectable VMO curves and a table of mach number versus q.sub.c /P.sub.s, receives the measured altitude and airspeed information, determines VMO and mach number therefrom, and directly drives the VMO and mach number displays where q.sub.c represents the impact pressure and P.sub.s represents the static pressure. The measured altitude and airspeed signals are analog synchro signals. In order to drive the VMO display, the received analog altitude synchro signals are digitized in a synchro-to-digital converter comprising a single multiplying digital-to-analog converter for both sin .theta. and cos .theta. synchro functions, and fed to the microprocessor which verifies the appropriate VMO from the preselected VMO curve, and drives the VMO analog pointer via a stepper motor servo loop closed by the microprocessor.