20 
the setting of the take of the general homographic outline on the homolog-comparator 
becomes quite simple because each frame can assume the due swing in its plane, and it will be 
possible to set the nuclear points with their coordinates prescinding the non-coplanarity of 
the frames themselves (Fig. 15). The instrumental symmetry characteristic of the homolog- 
comparator, is also taken advantage of for this performance. Obviously the limitations of 
employ of the homolog-comparator when using oblique take arrangements are deducible 
  
  
  
Fig. 14. Nuclear projectivity in the oblique take arrangement. 
especially on the basis of the values of the nuclear points abscissi, for a given focal take 
distance. 
d) Performance as homologoscope. 
The homolog-comparator, when set up with the alidades in homological position 
finally allows the performance of the following operations: 
— 1st. Identification of the pairs of homologs in sterograms obtained from converging take 
arrangements with or without intrinsical symmetry such however that the coordinates 
of the nuclear points and the fulcrums abscissa r in the two photographic systems of the 
take dihedral do not exceed the following absolute values. 
ordinates v: + 200 mm 
abscissi u: - 510mm 
abscissa r: = 510 mm