  In this paper we show how a two dimensional fluid model can be used to
interpret data obtained from an inclined Mach-probe or a Gundestrup probe. We
use an analytical approximation of the solution of the differential equations
describing the relation between the plasma flow and the measured ion saturation
currents at the probe's surface. The parameters of this analytical solution are
determined by comparison with the exact numerical solution of the equations. In
this way we are able to measure the parallel as well as the perpendicular Mach
numbers over the whole parameter range with a minimum accuracy of 90%.
