  This is a short review of the physical ideas,algorithm for the calculation of
the phase transition pressure and some results of a semi-classical theory of
the behaviour of materials under high pressure proposed by P.Savic and
R.Kasanin.It is base on the Coulomb interaction,supplemented by a microscopic
selection rule and a set of experimentally founded postulates,and it has found
applications from DAC experiments to planetary structure modelling.
