a) the block adjustment was carried out by four students as a normal exercise 
in the framework of their practical training at the I.T.C. The time recorded has 
thus a very limited value only. 
b) The controlpoint No. 117 was incorrectly observed in Strip 4 and had a 
very large error (about 200 meters). To adjust for this large error in the initial set 
of transformed coordinates (of Strip 4 as well as strip 3), four iterations were required 
instead of the usual number of two iterations only. 
Of the given control points for the planimetry, point 292 was rejected in the 
fourth iteration (which was carried out in a scale 1:200) as it caused too great a tension 
in the mechanical lay-out. The point was then used as a section-corner only. 
4 — SOME DATA ON THE PKECISION OBTAINED 
Y-parallaxes. — The van den Hout programme includes the computation of the 
residual ¿/-parallax in each point. 
For the relative orientation 6 points (only) had been used. From the residual 
¿/-parallaxes in these points, a mean square value of 8 microns was found (from 6 n 
\\pp 
parallaxes and m 2 = — , where n is the total number of models). For the triangul- 
n 
ation points, however, a mean square value of 13 microns was found. 
Relative precision of the block-adjustment. — After the execution of the I.T.C.- 
Jerie Block adjustment, the following relative precision was found. 
Planimetry. 
a) From the 7X8 inner section-corner points (for each of which four sets 
of coordinates had been obtained) and from the 2X8 outer section-corner points 
along the north and south side of the block respectively (each having two sets of 
coordinates), 128 x, y differences (A) between values obtained in successive models 
of the same strip were computed. All points concerned are pricked points. 
2 
With m 2 A = , we found: m Aa . = 2,10 metres (32 microns) 
m A = 1,85 metres (28 microns) 
b) After averaging, per strip, the corresponding x, y values of the 56 inner 
section-corner points, these averages, together with the single sets of x, y coordinates 
of the 2x7 outer section-corner points along the east and west side of the bloch 
respectively, were compared laterally. 
From these 70 differences (A), with m 2 A = , we found: 
Heights. 
_S. 
A 70 
m^ x = 1.75 metres (27 microns) 
m/\ = 1,85 metres (28 microns) 
From 145 tie-points (mostly terrestral check-points) between adjacent strips, 
with m 2 A = , we found: m A/j = 1.85 metres (0.23 % 0 Z). 
145