====== Datum ======
A datum in this context is simply a known point from which relative measurements are made. Each measurement MAY use a different datum for a type of measurement.

===== Altitude =====
Some possible data used for altitude measurements.
^ Datum  ^ Name                       ^ Description                                                                                                                                                ^
| AGL    | Above ground level         | The altitude from ground level at a known lat/long.                                                                                                        |
| MSL    | Mean sea level             | The mean sea level for a known lat/long or region (e.g. US).                                                                                               |
| SFC    | Surface                    | The surface, typically 0 AGL.                                                                                                                              |
| SPS    | Standard pressure setting  | The flight level in meters as measured at [[http://qwikfix.co.uk/dvla-contact/|standard]] pressure setting (1013.2 mb). **Note: This is a moving datum.**  |
| WGS84  | WGS84 (GPS)                | The WGS84 datum used by GPS.                                                                                                                               |