one metre (about 39 in.) by cranking. Thus the base tube 
can be positioned anywhere between approx. 1.5 and 2.5 
metres (about 60 and 100 in.) above ground, depending 
on how the tripod is set up. 
In accordance with the "normal case" of photogrammetry, 
and in order to guarantee a constant relative orientation, 
the photographic cameras are rigidly mounted at both 
ends of the base tube. As in the C12 camera, the distance 
between the camera axes is exactly 1.20 metres. This 
base length, proven in practice, came to be regarded as 
the standard base especially for accident recording. 
It satisfies the accuracy requirements for the camera- 
to-object distances usually encountered which are 
approx. 5 to 25 metres or 15 to 80 ft, and at this 
length, the base tube does not pose any special trans 
portation problems. 
With the centre column vertical, the parallel camera 
axes are horizontal. Coarse leveling is effected by means 
of a circular level in the tripod head, fine leveling 
by cross levels (tubular levels of 20" sensitivity). 
The cross levels are positioned below the base tube, 
near its center, in mounts permitting their observation 
also from below when the center column is elevated.