The SSD-120-30N altitude digitizer is designed to be mounted within a pressurized or non-pressurized, but temperature controlled area within aircraft operating up to 42,000 feet MSL. Usually remotely located, the digitizer is fully automatic in operation. The parallel ICAO altitude data output is controlled by the transponder. Trans-Cal SSD120-30N Benefits Best Warranty in the business: 42 months manufacture direct replacement. If your Trans-Cal encoder experiences a warranty covered failure, Trans-Cal will replace your unit with a brand new unit with a new 42 month warranty. Average MTBF: 9.7+ years. That's right Trans-Cal encoders are among the most reliable on the market, commonly providing reliable service for over 10 years. Pin for pin replacement for most other manufacturers encoders. Optional: Available with adapter plates that will allow the installer to mount the unit in another manufacturers mounting tray.