an index of 0 will indicate the time direction and indices and (going from 1 to 3) will indicate spatial directions. In Einstein's theory, the values of these parameters are chosen (1) to fit Newton's Law of gravity in the limit of velocities and mass approaching zero, (2) to ensure conservation of energy, mass, momentum, and angular momentum, and (3) to make the equations independent of the reference frame. In this notation, general relativity has PPN parameters and Alpha-zeta notation In the more recent notation of Will & Nordtvedt (1972) and Will (1981, 1993, 2006) a different set of ten PPN parameters is used. is calculated from The meaning of these is that , and measure the extent of preferred frame effects. , , , and measure the failure of conservation of energy, momentum and angular momentum. In this notation, general relativity has PPN parameters and The mathematical relationship between the metric, metric potentials and PPN parameters for this notation is: where repeated indexes are summed. is on the order of potentials such as , the square magnitude of the coordinate velocities of matter, etc. is the velocity vector of the PPN coordinate system relative to the mean rest-frame of the universe. is the square magnitude of that velocity. if and only if , otherwise. There are ten metric potentials, , , , , , , , , and , one for each PPN parameter to ensure a unique solution. 10 linear equations in 10 unknowns are solved by inverting a 10 by 10 matrix. These metric potentials have forms such as: which is simply another way of writing the Newtonian gravitational potential, where is the density of rest mass, is the internal energy per unit rest mass, is the pressure as measured in a local freely falling frame momentarily comoving with the matter, and is the coordinate velocity of the matter. Stress-energy tensor for a perfect fluid takes form How to apply PPN Examples of the process of applying PPN formalism to alternative theories of gravity can be found in Will (1981, 1993). It is a nine step process: Step 1: Identify the variables, which may include: (a) dynamical gravitational variables such as the metric , scalar field , vector field , tensor field and so on; (b) prior-geometrical variables such as a flat background metric , cosmic time function , and so on; (c) matter and non-gravitational field