small ring on the right side of the cursor was used to accurately place markings on the compass using the grease pencil. The face of the compass was then rotated to the aircraft heading, which caused the dot to move. The resulting position indicated the wind speed and direction. A holder for the pencil and a sharpener blade were attached on the left side of the case. The third method of determining the wind is used in conjunction with the wind gauge bar. The aircraft is flown on three different headings, typically 120 degrees apart, and the time for the aircraft to travel a certain distance was measured with the timing beads. The bearing plate was rotated to match the compass heading of each leg, and the cursor was moved along the bar to draw a line on the bearing plate along that direction. After three such measurements, a small triangle was formed. The aircraft then turned onto the bomb line. Using the drift angle measured from the auxiliary drift bar, the compass was rotated to that drift angle, and the cursor moved so it lay above the center of the triangle. This indicated the direction and speed of the wind. Other details Levelling the bombsight was required before any use. The bombsight included two spirit levels for this, and was mounted to a friction-set ball so it could be rotated in any direction. This allowed it to be mounted to the side of aircraft like the Supermarine Walrus, or to the floor of dedicated bomber aircraft like the Bristol Blenheim. As the most common change in angle is due to changes in aircraft trim with changes in airspeed, earlier models featured a prominent setting for correcting the fore-aft angle of the sight, which can be seen on the left side of pre-Mk. VII models in the images above. Naval versions of the Mk. VII and IX, and most supplied to Bomber Command as well, included an additional adjustment for moving targets. Attacking a moving target is similar to the basic concept for correcting for wind, although, unlike wind, the target's movement may be significant even after the bomb is dropped. The CSBS accounted for this through the use of the enemy vector mechanism or fourth vector, which was similar to the wind mechanism but operated at the origin of the drift bar instead of a point located along it.