use two « test » original negatives. In order to have in these « tests »
the entire transparent field, they can be submitted to well known
inversion baths. To avoid the inversion, which is preferable, 21
the moment of the impression of the «test » there can be applied
to the taking camera an opaque screeen (preferably metallic) imme
diately underneath the focal plane, this screen having small holes
situated in accordance with in the reperes.
The plotting instrument must posses adequate attachments (screws,
levers or similar) for the purpose of moving the photogram in the
right plane so that one of its marckings will coincide exactly with
a corresponding one of the « test » which is situated closer to the
zone in which the plotting takes place. The movement of the pho
togram, rather than manually can be achieved in an automatic and
progressive fashion between one repere and the next, if the device
is supplied with adequate components which for example the Ste-
reocartograph Santoni Mod. V is provided with.