proach, that is unless the ship gets off-course. 
Or, in other words, if the target wanders la 
terally, the large angular magnification in 
the distant target permits to determine and 
correct even very slight deviations from the 
true course at the beginning. A by-product of 
the synchronization of the crosshairs is the 
ground speed which can be read on a scale of 
the instrument. 
Navigational Procedures : 
1. Maintenance of straight-course lines of 
flight in a definite geographical direction. 
With the automatic pilot system incipient 
deviations from the true course set on the in 
strument are instantly checked and corrected 
by gyro control. Contrary to stick control, 
the flight track does therefore not meander 
on either side of the desired course but is a 
perfectly straight line. 
The gyro-pilot which may have deviations 
up to 3° from the true course within a quar 
ter of an hour, is supported by the compass. 
In last analysis, it is therefore the accuracy 
of the compass which determines the main 
tenance of a certain geographical direction of 
flight. In addition to the individual corrections 
of the compass which have already been men 
tioned, allowance must also be made for the 
magnetism of the earth. On long runs, espe 
cially in the east-west direction, the decli 
nation may change to a marked extent. The 
corresponding corrections of the heading 
must therefore be set on the automatic pilot 
at certain time intervals during the run. They 
may be previously computed fo V2 degree 
intervals of the declination from isogonic 
charts. 
The experience of numerous missions has 
shown that wind conditions at high flight 
altitudes over extensive areas are more or less 
constant. In other words: large “wind oc 
eans“ having the same direction and speed 
of flow are prevalent. As photoflights are 
generally made during very stable weather 
conditions, no appreciable change will usual 
ly be noticed during the entire time of the 
photoflight, that is 5 to 7 hours. It may therefore 
be assumed that the wind components ascer 
tained by drift measurements before starting 
on the first run will generally remain con 
stant for several flying hours. New determi 
nations of the wind conditions will be made 
in those places where a particularly conspi 
cuous landmark is directly on the course at 
the end of the run. After the wind data have 
been ascertained, this landmark will permit 
to pick up the end of the previous run for 
the purpose of correct matching of the strips. 
When the airplane has reached the photo 
graphic flying height, it flies a triangle with 
the aid of the automatic pilot to determine 
the wind data. The drift is measured on the 
3 courses which are at an angle of 120° with 
reference to each other. 
The wind computer (Fig. 4) then supplies 
the “wind point“ which is the point of gra 
vity of the triangle plotted from the 3 re- 
6