Experimental and theoretical values of local velocity and density were determined at several axial planes within the cylindrical throat region of a standard ASME, long radius, low beta ratio nozzle. The nozzle was calibrated in compressible flow (air) over a range of throat Reynolds numbers from 500,000 to 4,000,000 and over a range of throat Mach numbers from 0.4 to critical. The nozzle was calibrated in incompressible flow (water) over a range of throat Reynolds numbers from 170,000 to 1,600,000. The behavior of the observed nozzle discharge coefficients is interpreted.