The ALT-3 is a 3 1/8” instrument that contains a precision altimeter and a wide range vertical speed indicator. The altimeter conforms to ANSI standard atmosphere rules from –700 ft up to a maximum of 30,000 ft. The altimeter includes an encoding serial RS232 output AS WELL AS a parallel Gillham code output for direct connection to mode-C transponders.
The altimeter can display altitude in feet or meters, local pressure can be set in millibars or inches of mercury
The onboard VSI indicator is altitude compensated and can be displayed in either feet/minute (ft/min) or meters/second (m/s).
It also offers a digital readout with a wide range from +/-20 ft/min to as high as +/-10 000 ft/min, it also offers a logarithmic analog display with a +/-2000 ft range. The VSI can be calibrated by the user once the instrument has been installed in the aircraft.
In addition the ALT-4 provides an OAT sender which is used in the determining the density altitude of the aircraft. The ALT-1 can also be used to measure relative altitude as well as it has a facility for the pilot to enter a reference altitude and deviation band that has to be kept.