moves the height slider up or down to set the aircraft's altitude. Once set, the angle between backsights on the height slider and foresights on the ground speed slider indicates the proper range angle, no lookups required. The bomb aimer then sights along this angle and waits for the target to appear, dropping the bombs when it appears under a notch in the backsight. Although a bomb's trajectory is roughly parabolic, when the bomb is dropped from high altitudes it may reach terminal velocity before hitting the ground. This affects the final trajectory in a non-linear fashion, generally making the line of fall more vertical. To account for this a trail screw was added starting with the Mk. II version of the CSBS, which rotated the height bar forward. This had the effect of reducing the range angle, which accounted for the more vertical trajectory of the bombs. This effect only comes into play for high altitudes when the bomb has time to build up speed. Later models of the CSBS, starting with the Mk. VII, used a cam that was driven by both the altitude setting and the trail screw in order to automate the calculation of this effect. Additionally, each aircraft has a slightly different way of measuring altitude that needs adjustment, the CSBS accounted for this effect by including two altitude scales, a linear scale of altitude in orange on the right side of the bar, and any number of white scales on the back that could be clipped onto the sight. The two were used in combination to make adjustments for the altitude of the target over sea level. Practical example The operation of the CSBS is best understood using a simple example. For this the windage triangle shown in the section above will be used, combined with the operational description from AP1730. The problem for the bomber is to approach a target located at the tip of the green arrow, compared to its current position at the base of the arrow. A powerful wind is blowing from just off the port wing of the aircraft, blowing towards about 120 degrees. If the aircraft simply points toward the target, along the green arrow, the wind will cause it to drift to the right. In order to approach the target properly, the aircraft needs to turn to the left until the portion of its airspeed equal to