When a Helmet-Mounted Display (HMD) system is used in an aircraft cockpit, the usual intent is to overlay symbols or images in the display on their real-world object counterparts. The HMD system determines a pointing angle (in aircraft coordinates) to the real-world object. This pointing angle is sent to the Mission Computer (MC) for use by other aircraft systems and is used by the HMD to position symbology in the HMD image. The accuracy of the HMD is defined as the error of the pointing angle sent to the MC versus the real-world angle to the object. This error is usually given in terms of milli-radians (mrad). Note that having the symbol in the HMD image overlay the corresponding object in the real world does not necessarily ensure an accurate pointing angle. One example of HMD use is to position an aiming cross in the display over an aircraft in the sky. The pointing angle to that aircraft is sent via the MC to another sensor (radar, missile, targeting pod) which then locks onto that aircraft or object. The accuracy requirement is to get the other sensor pointed at an angle to detect the same aircraft. There are aircraft integration issues to ensure target acquisition, but these will not be covered in this paper. One component of the HMD system is a tracker system, and the tracker system's accuracy is often looked at as the HMD accuracy. However, the accuracy of the tracker system is only one piece of the total HMD system accuracy, and as trackers get better, they may not even be the largest error component. This paper identifies the various error components of the HMD system installed in the aircraft cockpit and discusses the techniques used for minimizing errors and improving accuracy.