BOMBARDIER Wings

A drop bomb (point down) superimposed on a circular target at the center of the wings.

From my copy of "The Official Guide to the Army Air Forces" handbook.
Allow me to paraphrase from this reference book...

The bombardier operated the bombsight, (which was about the same size of a typewriter), after he had computed data and set the mechanisms. The bombsight determined the correct point in space (and the specific type of bomb) that was to be released on the target. The fundamental data, set into the bombsight, was determined by the plane’s altitude above the target, ground speed, and bomb type used.

This data was figured by the bombardier before reaching the target area. Once on the bomb run, the bombardier’s technique determined if the bomb would hit the target or not. Through its telescopic mechanism, the bombsight established an angle between the plane and the target. This angle, varying with altitude, determines the distance from the target at which the bomb must be released. The computing of this distance was called the "range". Errors in computation caused the bomb to fall short or go beyond the target.