his paper presented to the 10th International Congress of Photogram- 
metry held in Lisbon [3]. 
Mr. Le Divelec had used, for the plotted model orientation, the same 
control points employed by Mr. Môller. The numerical and graphic 
plotting of the said model had been carried out 25 times. These plot- 
tings were carried out by using a same plotter(Stereocartograph Galileo- 
Santoni Model IV no. 030 b 00030) by 5 different operators having a 
practical working experience between 5 and 25 years. 
Each of these 25 plottings has been performed giving an altered value 
to the control points coordinates. In fact the alteration may be considered 
as an error introduced in the establishment of control point position on 
the ground. 
To point out in the best way the effects of these alterations in the photo- 
grammetric plotting, Mr. Le Divelec had assumed a total horizontal 
mean square error of + 0.80 mm and a vertical one of + 0.30 mm. 
The choice of the alterations introduced on the coordinates X, Y, Z of 
the 5 control points was made at random, keeping into account the 
normal distribution of errors in relation to the above said mean square 
values. 
The work performed by the 5 plotting operators has required the rela- 
tive and absolute orientation of the model, so as to approach as far 
as possible the machine coordinates of control points to their altered 
ground coordinates, and the numerical and graphical plotting of the 
model taken each time into consideration. 
The relative orientation of the photograms has been carried out through 
an empiric optical mechanical proceeding, derived from Von Gruber 
method, with the purpose to make the tests follow the method usually 
employed in a normal plotting work. 
The relative orientation has been considered concluded when the resi- 
dual'parallaxes, read on the 6 classical points, have resulted less than 
0.04 mm. 
Having formed the models, their absolute orientation has been carried 
out on 5 known points having altered ground coordinates, adopting a 
model scale of 1:4000. 
The model orientation (according to the situation rised every time by 
the altered control points) has been performed through an empirical pro-