Temporal evolution of the total kinetic energy E_kin(t) relative to its initial value E_kin(0) in the Gresho vortex problem. For different initial Mach numbers simulations were run with (solid) and without (dotted) flux preconditioning. The lines for the preconditioned scheme show very low dissipation and are virtually indistinguishable, that is, independent of the Mach number. The final values are listed in Table 1.