Reticle

A reticule or reticle is a shape superimposed on an image that is used for precise alignment of a device. Crosshairs are most commonly represented as intersecting lines in a "+" shape, though many variations exist, including dots, posts, circles, scales, or chevrons. The reticule is the primary means by which players (and Spartans, Marines and Elites) aim their weapons. It is located in the center of the screen and changes based on which weapon the person is wielding.

Overview

 * Normally blue in color, the reticule will change to red if moved over an enemy or green if moved over an ally. Note that if the enemy is not in range for that particular weapon, the reticule will still remain as blue. This is often a good indicator of an enemy being out of range. Zooming in (if your weapon has a scope attachment) may well make the reticule red if moved over a previously out of range enemy.
 * Note: The green ally reticule function was not introduced until Halo 2. As such it does not appear in Halo: Combat Evolved. The reticule simply remains blue.
 * If the weapon you are wielding is capable of a head shot, and the reticule is moved over the head of an enemy, a small dot will appear in the center of the reticule (with the exception of the beam rifle). This can help inexperienced player become more skillful in head shots
 * When dual wielding weapons, the two reticules for the two different weapons you are wielding will be laid on top of one another. While you are dual wielding two of the same weapon, the reticule will be no different than if you were wielding one of that weapon.
 * In Halo 2, the rocket launcher is a special case in terms of reticule, it will change when moved over an enemy vehicle, indicating the ability to "lock-on" to that vehicle. See the rocket launcher page for more information. A similar function is seen on the missile pod in Halo 3. This function is also seen in Halo: Reach with the Rocket Launcher, the Plasma Launcher and the Needler.
 * In Halo 3 and Halo 3: ODST, when a charged Plasma Pistol is aimed at an enemy in range, the reticule will shrink, notifying the player of when to release the trigger. In Halo: Reach, a second, smaller reticule will appear inside the regular reticule.

Tips

 * While the reticule is primarily for determining if you are aiming well or not, it can also be used to determine the spray of your weapon. Weapons such as the sniper rifle are very accurate and do not have a spray pattern or area of effect, so the reticule is very small, but weapons with a larger spray, such as the shotgun or the Warthog turret have much larger reticules. If the torso of an enemy fully occupies your reticule, you can be sure that an instant kill with one of these weapons is a distinct possibility. This also applies in general, usually the optimum range for a weapon is when the torso or head of your opponent fully occupies your reticule.
 * Remember also that the reticules of different weapons are different for a reason. Weapons such as the Brute shot are much easier to aim if you know how to use the reticule to help you to aim it.
 * The color of the reticule can also help you determine if the weapon is in range of the auto-aim. If your reticule is not red, the magnetic targeting will not work, making it harder to aim. Weapons like the battle rifle can achieve greater auto-aim range when scoped.
 * In Halo: Reach there is an improvement to the reticule called the Reticule bloom, this is where sustained fire will decrease the accuracy of the weapon being fired and also increases the size of the reticule. A way to stop this is to use short, controlled bursts of your weapon to make sure the bloom doesn't get too big. This is being removed, optionally or all-together, along with other changes, in the title update released by 343 later this year to accompany Halo: Combat Evolved Anniversary