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tance and can be caused by several factors, which must be kept under control (the form of the supporting 
plate in the camera magazine, the thickness of films and emulsions, the flatness of negative and diaposi 
tive plates). Tolerances have to be established and applied in practice to material, instruments, operators 
and methods. Similar standards can be applied to the reconstruction of bundles of rays from photographs. 
Tolerances are necessary for a rational supervision of instruments at time of delivery and during practical 
work. For the establishment of such tolerances the basic accuracy characteristics of instruments must be 
carefully determined. 
The work reported in this paper must be regarded as introductory. It seems necessary for the sound 
development of photogrammetry that much more attention should be devoted to the fundamental 
problems and that this work should be strongly coordinated with practical tests of the final results of the 
photogrammetric procedure. International organizations like the I.S.P. could without doubt, make very 
important contributions to the general developement if basic and applied research is combined as indi 
cated.