One can also leave the wire as it is, and turn the whole instrument instead. The angle of deviation is to be read on the instrument’s base. This is the easiest way, as it allows one to get on quickly with measuring the speed. Having calculated the deviation, it is not correct to steer against the wind allowing only a corresponding number of degrees, or it will be found that there is _still_ a deviation, though not so great as before. To correct it it would have to be measured, then some steering would have to be done, then it would have to be measured again and so on, before it could be regulated. It is, therefore, better to come to a quick and exact result by quickly taking the speed measure. This is done with the same instrument, by watching an object pass between four points of the scale, as the machine goes over it. The pilot continues to fly in a steady course during the entire observations. The navigator sets a stop clock going when an object passes the scale at an angle of 45°, and he stops the clock when the object passes zero, as it will then be centrally under the machine. The altitude above the under-lying territory is read on the altimeter, and by aid of this and the stop clock’s indications it is possible to calculate correctly the speed over the ground-distance covered. We have now got the following particulars: The speed through the air which the speedometer shows and which is called the air-speed,--the steering course through the air which we will call the air-course,--the speed over the ground which we will call the ground-speed and last the deviation’s angle. These calculations have to be worked out in conjunction with each other on a calculating machine, showing in a second what steering-course shall be adopted under the existing wind conditions, to carry the plane in the desired direction. In addition to this there is a gratis enlightenment, showing the exact direction and strength of the wind at that altitude. [Illustration: MOUNTING THE WINGS] [Illustration: THE LAST MEETING BEFORE THE FLIGHT] The pilot announces if a new course shall be steered. If he steers according to the solar-compass, the navigator adjusts the solar-compass by turning the periscope a corresponding number of degrees.