  This report proposes the solution of the long standing problem regarding the
key property governing the pressure related dynamics in glass forming and
complex systems: the determination of the apparent activation volume Va and its
pressure dependence. Results are tested in the previtreous domain, up to P ~
1.2 GPa, for glass forming diisobutyl phthalate (DIIP, low molecular weight
liquid), isoctyloxycyanobiphenyl (8*OCB, liquid crystal), bisphenol
A/epichlorohydrin (EPON 828, epoxy resin).
