for the sights, the so-called range angle, and set the sights to that angle. This solution was far from practical, and prone to error. In 1916, Harry Wimperis started the design of a new bombsight, working in collaboration with Scarff. This new Drift Sight included a simple system that greatly eased the measurement of the wind. By observing their movement over the ground, the aircraft would first determine the direction of the wind. The aircraft would then turn to fly at right angles to this wind direction so that the wind was pushing the aircraft sideways. Observing the sideways drift of the aircraft by comparing the motion of objects on the ground to a metal rod along the side of the bombsight, the drift could be seen. Using a knob, the rod was angled away from the side of the aircraft until objects could be seen moving directly along the line of the rod. A gear in the knob that adjusted the rod angle also drove the sights fore or aft, moving them to account for the wind speed. This eliminated the need for a stopwatch to measure the ground speed. However, the Drift Sight was still useful only for bomb runs along the wind line. Course Setting Bomb Sight When an aircraft flies in the presence of wind, its flight path over the ground is a function of the aircraft's airspeed, heading, and the speed and direction of the wind. These are combined using basic vector addition to return the course made good or track. These calculations are a basic part of air navigation and dead reckoning, taught to all aviators. Wimperis was more than familiar with this topic, and would later write a well-known book on the topic. To aid in the necessary calculations, it was common to use a simple mechanical calculator that combined a slide-rule like calculator on one side with a vector calculator on the other. The best-known modern example is the E6B, which remains a basic part of every pilot and navigator's toolkit. Using the vector calculator and basic measurements, one can easily calculate the winds aloft and then the course made good. These calculations are identical to those needed to properly account for the effects of winds on the bombing approach. The problem was that these calculations were complex, time consuming and error prone. Wimperis decided to attack the calculation problem by incorporating