Elevation is the angle a gun barrel is rotated up from horizontal so that its shell will arc upward. Higher elevations generally cause the shell to fly to a longer range. The relationship of a gun's elevation when loaded with a particular shell and powder charge was recorded in a range table used to create sighting equipment for the weapon.
Guns of any appreciable size generally had a man (called a gunlayer in the Royal Navy, and a gun pointer in American parlance) who set the gun to elevation for firing, typically by use of a geared handwheel or a hydraulic valve.
The means by which the proper elevation was calculated, conveyed and established on the weapon was one facet of the problems of sighting and fire control.