  A new procedure for the reduction of "Carte du Ciel" plates is presented. A
typical "Carte du Ciel" plate corresponding to the Bordeaux zone has been taken
as an example. It shows triple exposures for each object and the modelling of
the data has been performed by means of a non-linear least squares fitting of
the sum of three bivariate Gaussian distributions. A number of solutions for
the problems present in this kind of plates (optical aberrations, adjacency
photographic effects, presence of grid lines, emulsion saturation) have been
investigated. An internal accuracy of 0.1'' in x and y was obtained for the
position of each of the individual exposures. The external reduction to a
catalogue led to results with an accuracy of 0.16'' in x and 0.13'' in y for
the mean position of the three exposures. A photometric calibration has also
been performed and magnitudes were determined with an accuracy of 0.09 mags.
