Inclination is the angle a target ship's heading forms to the line of sight of an observer. An inclination of zero degrees implies the ship is steaming away from the observer, and 90 degrees means he is steaming orthogonally to the line of sight, left to right. Inclinations are generally expressed in the range -179 to 180.
Because targetHeading = compassBearing + inclination, a target's heading is implied by his inclination provided his compass bearing is separately known, but does not impose upon the person reporting the inclination the burden of knowing the bearing or performing arithmetic. In most cases, the conversion of an inclination to an enemy heading is facilitated by use of a dumaresq or a similar instrument.