When adjusting the sheaf for mortars, what does the observer base their determination on?

In adjusting the sheaf for mortars, the observer bases their determination primarily on wind direction. Wind plays a critical role in the trajectory of mortar rounds, as it can significantly affect the accuracy and impact point of the rounds fired. Understanding the wind direction allows the observer to compensate for any drift that might cause the rounds to land outside of the intended target area.

By knowing the wind speed and direction, the observer can make adjustments to the firing data, ensuring that the mortar fire is effective and on target. Other factors, while they may influence the overall tactical situation or visibility, do not have as direct an impact on the adjustment of mortar fire as wind does. Therefore, wind direction is the most relevant factor for adjusting the sheaf in this context.