"At-sea alignment" is a synonym for inertial high technology and
computing. An aircraft carrier has an inertial navigation system "hybridized" with GPS information (and even an electromagnetic log). It gathers optimal geographical positioning, speed information with regard to the ground, acceleration and angular velocity from ship’s master reference system. This navigation information can’t be used directly to align aircraft’s navigation system as it requires certain re-computation depending upon location of aircraft with respect to ship’s MRS. Once these computations are done, same information gets forwarded to aircraft’s navigation system on its
compatible protocol. In the aircraft, an inertial system, also hybridized with GPS, receives this information from the aircraft carrier system and uses it to initialize its position, speed and acceleration, despite the "lever arm" which exists with regard to the ship's navigation unit. This is the basic operating principle of "at-sea alignment".

NELM was the first customized product designed for Indian Navy. It receives navigation data from ship-borne INS, recomputes it for takeoff position of helicopter and generates all necessary
information for INS alignment process before take-off.