  Firing Squad Synchronisation on Cellular Automata is the dynamical
synchronisation of finitely many cells without any prior knowledge of their
range. This can be conceived as a signal with an infinite speed. Most of the
proposed constructions naturally translate to the continuous setting of signal
machines and generate fractal figures with an accumulation on a horizontal
line, i.e. synchronously, in the space-time diagram. Signal machines are
studied in a series of articles named Abstract Geometrical Computation.
  In the present article, we design a signal machine that is able to
synchronise/accumulate on any non-infinite slope. The slope is encoded in the
initial configuration. This is done by constructing an infinite tree such that
each node computes the way the tree expands.
  The interest of Abstract Geometrical computation is to do away with the
constraint of discrete space, while tackling new difficulties from continuous
space. The interest of this paper in particular is to provide basic tools for
further study of computable accumulation lines in the signal machine model.
