English: Martin MB-2 (NBS-1) bombardier compartment with Estoppey D-1 bombsight, adjusted to compensate for wind drift.

The dial on the far left is used to adjust for the wind, rotating it causes the entire sight to rotate to the left or right. In this particular setup, it has been rotated some distance to the right, indicating a wind from the left. The operator turns the sight until the target can be seen travelling directly down the long wire running parallel to the right side of the device. The large needles at the front of the device and its holding frame are used to quickly determine the drift angle, about 10 degrees in this case.

Before the drop, the operator uses the large cylindrical dial at the rear (bottom in this image) to set a countdown stopwatch inside the device. This is set to the time it takes for the bombs to reach the ground from their current altitude. The dial also has secondary settings to adjust for wind or the speed of the target, but these were estimated by the operator and not part of the calculations made by the device itself.

The main operating crank is visible to the left of the middle of the image. After setting the timer, the crank is turned clockwise (rearward) to place the frontmost of the three cross wires to indicate the distance that the bombs would travel forward after being dropped from this altitude. This is normally on the order of hundreds of meters. The operator then sights through the upper wire, the middle one in this image, to the foresight. When the target passes through that line, they begin turning the crank counterclockwise (forward), which turns on the timer and causes the foresight to begin moving rearward. They turn the crank to keep the target along the sightline as the bomber moves towards the target.

When the timer runs out, the crank is disconnected. This means the sights have moved through the angle that the target moved during the time it would take the bombs to drop. Due to the wind, this is not necessarily the same distance that was previously looked up. By directly measuring this motion the system takes into account both the wind and the motion of the object.

Turning the crank also moves the rear lower sight, the rearmost one in this image, forward at the same speed. This leaves in the correct location to drop the bomb after accounting for wind. The operator then shifts their line of sight from the top and front sights to the top and rear. When the target passes through this second line they drop the bombs.