state 1 that dp dc and that dp gt dc dc being the distance from the target to the firer the burst tracking table is formed by all the projectile tracking tables classified according to the indicator ic the burst exit table is formed on the basis of the burst tracking table by a list of words defining the tracers in the image the tracers are considered successively in the order of their increasing y ordinates and in the order of their increasing x abscissae in respect of one and the same ordinate the first tracer of the image is defined by a first word containing its ordinate and by a second word containing its abscissa each tracer having a smaller abscissa on the lines following that of the first tracer is defined by a first word containing the variation dy of its ordinate with respect to the ordinate of the first tracer and by a second word containing its abscissa each of the other tracers is defined by a word containing the variation dx of its abscissa with respect to the preceding tracer on the same line each word which contains in addition a digit dy indicates the presence in said word either of an ordinate or of a variation of ordinate in which case dy 1 or of an abscissa or of a variation of abscissa in which case dy 0 each word containing an abscissa or a variation of abscissa contains in addition the data l de and pdc relating to the tracer considered the operation of the calculator cn takes place in accordance with a program comprising four successive periods having orders p p 1 p 2 and p 3 having.