The predicted impact point (PIP) is the location at which a ballistic projectile (e.g. bomb, missile, bullet) is expected to strike if fired. The PIP is almost always actively determined by a targeting computer, which then projects a PIP marker (a "pipper") onto a Head-Up Display (HUD). Because of the way modern HUDs are focused, the weapon operator will see the marker projected directly over the point of impact, regardless of the position of his eye.
Modern combat aircraft are equipped to calculate the PIP for onboard weapons at any given time. Variables that are included in the calculation are aircraft velocity, target velocity, target elevation, distance to target, forces on the projectile (drag, gravity), and others. Using the PIP marker, pilots can achieve good accuracy at ranges of up to several kilometers, whether the target is ground-based or airborne.
"Red dot" optical firearm sights like the M68 Aimpoint are another example of devices that show the PIP. Such sights project a glowing red dot between their lenses. Like on a HUD, the dot always appears over the weapon's impact point, regardless of the position of the shooter's eye. Red dot sights do not use internal computers and must be manually zeroed for maximum accuracy.
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