text: In a coordinate system that is moving with the discontinuity, the Rankine–Hugoniot conditions can be expressed as:
  where m is the mass flow rate per unit area, ρ and ρ are the mass density of the fluid upstream and downstream of the wave, u and u are the fluid velocity upstream and downstream of the wave, p and p are the pressures in the two regions, and h and h are the specific (with the sense of per unit mass) enthalpies in the two regions. If in addition, the flow is reactive, then the species conservation equations demands that
  to vanish both upstream and downstream of the discontinuity. Here,  is the mass production rate of the i-th species of total N species involved in the reaction.
  Combining conservation of mass and momentum gives us
  which defines a straight line known as the Michelson–Rayleigh line, named after the Russian physicist Vladimir A. Mikhelson (usually anglicized as Michelson) and Lord Rayleigh, that has a negative slope (since  is always positive) in the  plane. Using the Rankine–Hugoniot equations for the conservation of mass and momentum to eliminate u and u, the equation for the conservation of energy can be expressed as the Hugoniot equation:
  The inverse of the density can also be expressed as the specific volume, . Along with these, one has to specify the relation between the upstream and downstream equation of state
  where  is the mass fraction of the species. Finally, the calorific equation of state  is assumed to be known, i.e.,