40 
3.1. 
8. 3. 
taken into account. In the short triangulations of the type to be considered for 
the large scales — of 8-12 couples — it is to be expected that the operations are 
not greatly influenced by a modification of the stability of the restitution instru- 
ment. Therefore nothing has been prescribed to the Centres for the preliminary 
tests on grids and the stability tests of the instruments. 
The observation forms on which the Centres must register the observation results 
at the moment that they are carried out, are identical to those adopted for 
Comm. A. 
Two carbon copies will be made of them of which one must be sent to the Bureau 
Exécutif each week and the other to the President of the Commission. 
At the end of the month a short report about the progress of the work and the 
difficulties encountered shall complete the documentation to be sent to the Bureau 
and to the Presidency. 
Direct contacts by correspondence between the Centres and the Bureau or the other 
Centres will permit to overcome quickly the difficulties of detail which occur 
during the tests. 
The experimental material to be sent to the Centres comprises the series of dia- 
positives of strips to be triangulated, coordinates of three points determined on 
the ground for the putting in place of each first couple, the topographic descrip- 
tion of the control points to be measured during the triangulation, a series of 
paper prints with indication of the control points and the flight index maps. 
The definite instructions for the execution of triangulations on large scale pro- 
vide, after agreement between the members of the Comité Directeur and the 
Commission, the use of the free triangulation method, viz without conditions. The 
particulars of the chosen procedures are specified by the Centres. These methods 
form the object of a detailed description, supplied to the Bureau Exécutif and to 
the Presidency of the Commission before the start of the operations. 
An alteration of the method is permitted, but in that case the changes planned 
must be reported beforehand. 
The orientation of the first model is assured by the knowledge of the coordinates 
of five points placed in a suitable position. The exact coordinates of the other 
points, signalized and determined on the ground, shall be communicated to the 
Centres after the operations of triangulation have been achieved. 
The Centre to whom the taking of the photographs and the determination of the 
control points is entrusted, must send to the Centres, at the same time as the 
plates to be used, the first azimuth of each strip, the flight index maps and the 
definite numbering of the strips. 
The restitution operations must be started by using the predetermined starting 
data. The registration of the observed elements must be carried out on standard 
forms. 
The orientation of the couples must be started with base inside and in the direc- 
tion of increasing X. 
All other elements of orientation must be in position zero for the first couple. 
The enlargement in the instrument is determined by each Centre, taking into 
account the most favourable conditions of the instruments used. 
The choice of the scale of the model to be adopted is free and the Centres shall 
adopt it according to the characteristics of the restitution instrument used. 
In order to carry out the relative orientation one must use 6 points, distributed 
in the classical manner, in two transversal sections going through the extremities 
of the base.