479 
Conclusions 
1. No general conclusions can be drawn from these investigations 
since only four operators participated. Moreover, it must be empha 
sized that the results refer tq the precision of the setting in a stereo 
model. Throughout the experiment the same point was measured. The 
importance of alcoholic intake for the relative and absolute orientation 
and for the total photogrammetric procedure can hardly be judged from 
this investigation. 
2. The influence of alcohol varies from one operator to another 
(see tables 3 and 4) and the setting precision in the stereomodel seems 
not to be altered in any important amount (see table 4). 
3. The investigations have given information about some additional 
facts. 
3.1 A play of the y-screw of A8 was discovered and adjusted. 
3.2 A continuous displacement of some settings during the course of 
a day could be explained by the unsymmetrical form of the signal. The 
settings were successively altered. 
3.3 In some cases a smaller training effect could be observed during 
the first series, but also during the entire run of investigation 1. 
3.4 Bartlett’s test has shown that an operator sometimes changes his 
precision so much during a day that calculated standard deviations 
cannot originate from the same theoretical population. If the measure 
ments do not have the same precision, the assumptions underlying 
variance analysis and error propagation are often not at hand. (Va 
riance and regression analysis can be applied when the variance is a 
known function of the independent variable in the analysis.) 
4. It must be remembered that the setting precision, only, has been 
investigated. It is possible to increase the precision by averaging (s ave r a ge 
= s/ \/ n). The final accuracy of the photogrammetric procedure, 
however, depends upon the quality of the image coordinates, the re 
construction of bundles of rays, the relative and absolute orientation. 
The precision of settings is in general so high that it has very limited 
influence upon the final accuracy. The image quality seems to be the 
limiting factor at present. 
The precision of different method for Y-parallax elimination 
Introduction 
When the relative orientation of a stereomodel is performed in a 
photogrammetric instrument, the y-parallaxes are eliminated in the 
characteristic points of the model. The images and the marks can be 
observed in different ways and in this investigation three methods 
have been used: