The Agni-II's navigation and aiming uses an advanced ground-based beacon system using a TDOA (Time Delay Of Arrival) technique, similar to a GPS system, that constantly provides missile flight position and velocity updates and has been proven in test flights. The TDOA system reportedly improved the accuracy by three times. India has demonstrated a measure of mastery in navigation sensors and flight control through its space program. The placement accuracy in GTO (involving powered flight of 1,000 seconds much of it in sub-G or gravity free environment) is far more complicated and delicate than that of the sub-orbital trajectory of an IRBM. Thus the GSLV-D2 and F01 GTO Apogee accuracy of 1965 PPM and 361 PPM respectively that compares with Agni-II's 40 meter CEP at IRBM ranges with 13 PPM accuracy.