File:Course Setting Bomb Sight Mk. IXA stowed.jpg

English: This is an example of the Course Setting Bomb Sight Mk. IXA, a model used immediately prior to and during World War II. This example is folded down for stowage, with the "height bar" rotated forward over the drift bar on the left, and the "wind bar" rotated to lie on top of the height bar. The "auxiliary drift bar" has been folded to the right side of the drift bar, it is the object with the round holes punched in it. this example has several cutaway portions on the left to demonstrate its internal mechanisms.

On the left of the image, the compass has been cut open to show two horizontal gears. These are turned using the knob on the extreme left. Pushing down on the knob allows its own gear, visible in the separate cutaway, to engage the larger gears below the compass. One of these is connected to a rotating shaft lying just below the lower (brighter) gear. This shaft runs to the right through the silver coloured tube in the center of the image. Here it turns a vertical gear and shaft in the black housing at the right end of the tube, which in turn causes the black bar on top of the housing to rotate to the same angle. This mechanism allows the bomb aimer to adjust the wind direction using the knob, which will turn both the indicator in the compass, the black and white arrow, as well as the wind bar that carries out the actual calculation.

The two remaining major inputs to the calculation are the air and wind speed. Airspeed is dialled in using the large knob at the extreme lower center of the image. This turns a pinion that pushes against the rack, visible on the lower section of the silver coloured tube. Higher airspeeds cause the wind bar to be moved to the right. The wind speed is dialled in using the small black knob on the left side of the wind bar, which has white numbers on it for different speeds.