What adjustment factor is used when calculating the Height of Burst (HOB) for illumination rounds?

The correct adjustment factor for calculating the Height of Burst (HOB) for illumination rounds is the rate of descent. This factor is essential because illumination rounds are designed to provide light illumination for an area, and their effectiveness relies on the height at which they burst to disperse light over the desired area. The rate of descent indicates how quickly the illumination round will fall, which directly affects the timing for when it should detonate to achieve optimal lighting at the target area.

In contrast, other factors do not directly correspond to the specific requirements for illumination rounds. Ground speed pertains more to the velocity of the projectile rather than its burst height. Time of flight is related to the duration it takes for the round to reach the target but does not account for the specific descent characteristics necessary to determine the appropriate HOB. The OB factor, often used in the context of high-explosive munitions, does not apply to illumination rounds in the same way it does for other types of artillery. Thus, the rate of descent is the most relevant factor for ensuring effective illumination.