8 
PIERO BENCINI 
consisted of buildings, and were determined by direct multiple intersection from the 
points of the basic net. The horizontal observations were effected with four repe 
titions together with the measures of the basic net ; the zenith distances were mea 
sured three times each. 
The 112 points thus determined served as a base to determined 311 control 
points. Most of these were determined through inverse intersection, and only a 
small portion through direct or mixed intersection ; here again horizontal directions 
were observed by means of four repetitions and the zenith distances three 
times each. 
The ground materializations were carried out as follows : after excavating 
a hole about 50 -f 60 cm deep, we set therein a concrete bloc with sides of about 
20 cm, holding a zinc cap like a truncated cone (fig. 2) ; this was covered by a 
concrete cast and a piece of asbestos lumber pipe was set on top — of a diameter 
of about 10 cm — up to the ground level with the double function of protecting 
the centre and serving as a basis for the target pole, wherever necessary. 
Fig. 2 - Materialization of control points. 
For the surface markings we had prepared some quadrangular sheet of plastic 
cardboard, each side measuring 120 cm, printed on both sides as shown in fig. 3 
and having in the centre a hole of 10 cm diameter. They were nailed onto wooden 
pickets fixed into the ground the part with the appropriate colouring showed up. 
Fig. 3