For the Ronchi test, the phase of the Ronchigram can be retrieved very accurately with the aid of a phase-reduction algorithm originally designed for phase-shift interferometry. The simplest algorithm to reproduce the test wave front is the integration of the Ronchigram phase. However, the accuracy of integration depends heavily on the grating spacing. The effects of grating spacing is discussed using actual test results and mathematical simulation. The results indicate that coarse gratings, which benefited from the accuracy of phase-reduction techniques and qualified for integration in retrieving wave fronts, may be the better choice for the Ronchi test.