We propose to perform accurate measurements of the quantum gravitational effect for OffSpec. We would like to investigate if a similar discrepancy between quantum system gravity and classical gravity is found as in the 1975 Colella, Overhauser and Werner experiments (COW). We would like to use OffSpec because it is different from the COW experiments in many ways. For instance, we use a magnetic field and not a perfect crystal to split the wave function, which allows quite stable and distortion-free adjustment of gravitational effect. Accurate measurements of the phase plot need to be performed in horizontal and vertical geometry of the instrument. The instrument needs to be calibrated in both geometries using a reflection grating. This is already a standard procedure on OffSpec and the grating is present.