the wind speed cancels out the drift. The resulting direction is represented by the yellow arrow in the diagram above. On the CSBS each of these arrows has a mechanical equivalent in the bombsight. The direction of the yellow arrow is that of the aircraft itself, represented in the bombsight by its mounting to the aircraft fuselage. The length of the yellow arrow is set by rotating the air speed drum, carrying the windage calculator with it. The milled head is used to rotate the wind bar to the same angle as the wind, in this case about 120 degrees. This would leave the wind bar almost at right angles to the drift bar, with the wind speed knob easily accessible on the left. Finally, the wind speed would be dialled into the wind speed knob, which would push the entire drift bar assembly to the right. When all of the adjustments are complete, the bombsight and airspeed shaft mechanically represent the yellow arrow, the wind bar represents the blue arrow, and the green arrow is formed by the drift wires providing direction, and the foresight is positioned at the tip of the green arrow. Once set, the bomb aimer uses the rear sights, or any other convenient part of the bombsight, as a reference location and spots past them through the drift wires. Although these are now angled several degrees to the right, the wind to the right is pushing the aircraft so its final motion is along the wires. When initially set up the aircraft would likely be flying a course close to the green arrow, so the bomb aimer would see the targets drifting to the left relative to the wires. He would call the pilot and ask him to turn to the left and then watch the results. In some aircraft, a pilot direction indicator would be used. Several corrections are normally required before the aircraft is flying along the yellow line and the residual drift is entirely cancelled out. Measuring the wind Although the CSBS automated the calculation of the effects of the wind, it did not automate the measurement of the wind itself. The bombsight manual describes several ways to do this. One is an adaptation of the method used with the Drift Sight. Prior to approaching the target, the bomb aimer would have the pilot turn onto the expected wind line, and dials