0 
due to the omission of the second component will be?; 
•■«.55 
-IK 
H. 
‘kol 
420 
Me can somment this ratio that way;if we neglect the second component 
we commit the ralative error 7— at the model scale« In other words, we 
can say that a lenght of 420 mm will have the error of '1 mm. As we can 
see, this value is not to be neglected as the accuracy of scale is con 
cerned; none the less ±n this case too the scale of the stereogram would 
be very close to its real value. 
These considerations don i suggest, that the second component has to 
be neglected, they stress only the sightness of the method. In our expert- 
merit we have had many times, in the average conditions, the concordance 
in the scale of the stereogram, of the order of 0,1 mm on the passpoints. 
It means, that even without taking into account the second component we 
have had the complete graphical concordance. It was, of course due to the 
fact, that the air photographs were taken from the same height above the 
plane of reference. 
71* The principle of the conception of the outer orientation of air 
photographs 
Let 3 suppose, that we have the first stereogram of a strip of air 
photographs already oriented, according to the present methods on the 
basis of well disposed passpoints. 
Then we may adopt such a system and sequence of plotting, that the 
observer will see the area to be plotted so, that the western part of the 
area, will be always, for instance, on the left-hand side of the obser- 
ver. The adoption of such a system is convenient, because the observer 
can be easily oriented about the disposition of points and the content« 
of the map to be plotted. Thus, for the direction west-east of the strip 
one can adopt the beginning of the strip on the we3t side. Then we can