Heads-up display

Summary
The Heads Up Display unit, or know more clearly through it's acronym HUD, is a visor mounted display, and is one of the most useful elements present in the MJOLNIR Armor, coming just short of their Personal Energy Shields. The Heads-Up Display is the main source for information in-game on Halo: Combat Evolved, Halo 2 and Halo 3. The sensors augmented into the Spartan's body display the soldier's vital signs, which include a measure of their overall health in the form of bars. Note that this "health bar" has been removed from Halo 2 and Halo 3, with the reason being due to the insertion of automatic bio-foam injectors into the Mark VI armor. Additionally, the HUD also reports the strength of the wearer's shields through the energy signatures it emanates. Weapons heat and ammunition levels, as well as grenade type and count are also detected through sensors placed in the Spartan's gloves. In Halo 2, the Mark VI armor is able to register two weapons when the Spartan is duel-wielding. The Motion Sensor is another important feature displayed on the HUD. It can sense and track movement in a 15 meter radius (Halo 1), a 20 meter radius (Halo 2) and a 25 meter radius (Halo 3). The radar can also distinguish friend from foe, due to the IFF tags of other soldiers or enemies. Finally, way point indicators are an on screen directive that point out important elements or locations in the Spartan's mission, and are extremely useful, measuring the distance the Spartan is from the objective.

The appearance of the HUD has changed dramatically from Halo: Combat Evolved, Halo 2, and Halo 3. While the MJOLNIR Mark V HUD displayed a Spartan's health and shield strength readout on the upper right corner, this is absent from Halo 2 and Halo 3. In Halo 2 and Halo 3, the weapon selection and ammo counter has been moved to the upper right corner, while the grenade type and count was placed on the upper left corner (duel-wielding places the left-handed weapon in the top left corner). The shield strength was moved to the bottom right corner above the motion tracker in Halo 2, but changed to the top-center area in Halo 3. Halo 3 also saw the addition of a slightly convex appearance to simulate looking through a visor. Also, the MJOLNIR shields flare up in a grid-shaped pattern, to simulate the player is taking damage.

A HUD display is featured on SPI Armor, MJOLNIR armor, ODST Body Suits, Marine Body Armor, and even the Elite armor.

MJOLNIR armor, SPI armor, and Elite armor
The standard MJOLNIR armor contains the following readouts:


 * A meter displaying the relative Vitality of the user (absent from Halo 2 and Halo 3).
 * A gauge displaying Shield integrity status.
 * A gauge tracking the quantity of ammunition available for weapons carried.
 * A motion tracker.
 * A counter tracking the number and type of Grenades carried.
 * A targeting reticule which changes relative to the weapon currently in use.
 * Acknowledgment lights from other members of the wearer's team.
 * Maps and information uploaded over the wearer's TACCOM.
 * Zoom Function or function for using a Fiber Optic Probe (absent from Halo: Combat Evolved).

ODST Body Suit and Marine Body Armor
The standard ODST and Marine armor contains the following readouts:


 * A gauge tracking the quantity of ammunition available for weapons carried
 * A motion tracker
 * A counter tracking the number and type of Grenades carried
 * A targeting reticule
 * Acknowledgment lights from other members of the wearer's team
 * Maps and information uploaded over the wearer's TACCOM.

Trivia

 * It is unknown how the Elites see their HUD due to the fact that they have no visor or digital readout. A possibility is that they are able to view the information thanks to cybernetic optical implants.
 * Custom games in Halo 3 let you be able to change how far your radar reads (10 metres, 25 metres, 75 metres or 150 metres).