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«174 
The horizon camera, useful in determination of M and C2, 
should be included in the survey system when atmospheric condi- 
tions would likely allow the obtaining of horizon pictures of 
reasonable quality. 
Results achieved so far with auxiliary data are very encourag- 
ing. Nevertheless, further research and development in instru- 
mentation and adjustment techniques are essential. A number of 
instruments employed in the aerospace industry should be examined 
to determine their possible application as more precise stato- 
scopes and tip and tilt indicators. 
The behaviour of barometric pressure surfaces needs to be 
studied with the view of determining their shape more precisely 
under different conditions. 
Further development of adjustment methods and electronic 
computation programmes which accept coordinates of projection 
centers and angular orientation elements of the aerial photo- 
grophs, would contribute to a wider acceptance of auxiliary data 
and. improve the accuracy of final results. In this respect, it 
should be remembered that strip and block adjustment must pre- 
serve the high, relative accuracy inherent in each individual 
stereomodel. 
Finally, international experiments in aerial triangulation 
with auxiliary data over areas with an abundance of vertical 
control, should be encouraged. These tests would contribute to 
better knowledge and understanding of auxiliary data and its