The horizontal distance

The horizontal distance 

When an archer shoots at a target that is uphill or downhill, the distance to the target is different from how far the arrow travels horizontally. The horizontal distance is the flat distance the arrow covers without considering the height difference, and it is always shorter than the straight-line  distance to the target. Because gravity pulls the arrow downward regardless of the slope, the  archer should focus on the horizontal distance when aiming, rather than the direct line-of-sight distance.

To find the horizontal distance, you can use a math formula: it is the square root of the line-of sight distance squared minus the height squared. 

This principle is fundamental for accurate shot placement, as using the actual line-of-sight distance can lead to overshooting uphill targets or undershooting downhill ones.