TM 1-1520-238-10 Change 8 3-64.1 any of the coordinate data in the Navigation System. If alti- tude is not entered and the coordinate data is used to pre- point, the current helicopter altitude is used. The range of altitude entry is –900 to +20000 ft. MSL. b. Map datums. Map datums are mathematical mod- els of the Earth used to calculate the coordinates on maps and charts. Currently, many datums are used throughout the world to produce maps. The standard for US Forces is World Geodetic System 1984 (WGS 84). However, many US Military Grid Reference System (MGRS) and foreign maps are still based on other datums. Not correcting for different datums can cause significant errors. The coordi- nates for a point on the Earth’s surface in one datum will not match the coordinates from another datum for the same point. The Integrated Navigation System requires that the datum be entered with the coordinate data. If it is not entered, it will default to the present position datum. The datum included with each set of coordinate data al- lows the Navigation System to calculate the compensa- tions for different datums. Multiple datums can be used and the Navigation System will accurately generate the compensated navigation or prepointing data. The datum used is identified by a 2 digit number. Table 3-21 lists all of the datums that may be used with the Integrated Naviga- tion System. Table 3-21. Datum Names and Codes Datum Name/Description Datum Code Used By Navigation System Adindan 01 ARC 1950 02 Australian 66 03 Bukit Rimpah: Indonesia 04 Camp Area Astro 05 Djarkarta: Indonesia 06 European 1950 07 Geodetic Datum 1949 08 Ghana 09 Guam 1963 10 Gunung Segara: Indonesia 11 Gunung Serindung: Indonesia 12 Herat North 13 Hjorsey 14 Hu–Tzu–Shan 15 Table 3-21. Datum Names and Codes (cont) Datum Name/Description Datum Code Used By Navigation System Indian: Mean Value For Thailand And Viet–Nam 16 Ireland 1965 17 Kertau: West Malaysia 18 Liberia 19 Other International 20 Luzon 21 Merchich 22 Montjong Lowe: Indonesia 23 Minna 24 North American Datum of 1927 25 NAD 27 Alaska: Canada 26 Old Hawaii: Maui 27 Old Hawaii: Oahu 28 Old Hawaii: Kauai 29 Ordnance Survey of Great Britain 1936 30 Qornoq 31 Sierra Leone 1960 32 Campo Inchauspe: Argentina 33 Chua Astro: Paraguay 34 Corrego Alegre: Brazil 35 Provisional South American 1956 36 Yacare: Uruguay 37 Tananarive: South American 1925 38 Timbali: East Malaysia 39 Tokyo: Japan: Korea: Okinawa 40 Voirol 41 Special Datum: Indian Special 42 Special Datum: Luzon 43 Tokyo Datum 44 WGS 84 Special Datum 45 Sino–Soviet Bloc 46 WGS 84 Standard Datum* 47 * All FAA Sectionals and FLIP use this datum for coordi- nate data.