AUSGeoid98 has been replaced by AUSGeoid09 as the national geoid model for Australia. AUSGeoid98 was based predominantly on satellite and terrestrial gravity observations which were a best fit of the geoid over Australia (Featherstone et al 2001). Although AUSGeoid98 was designed to assist GPS users to convert ellipsoidal heights to AHD heights it did not account for the one metre offset trend between the geoid and the AHD. As a result, when using AUSGeoid98, GPS users could only retrieve AHD heights to within ±0.5 metres. Using AUSGeoid09, users can compute AHD heights to within ±0.03 m across most of Australia.