An MR measuring assembly (3) with an MR device (2) is provided, which has a main magnet (4) generating a stray magnetic field and a platform (1), having a side border (5), on which the MR device (2) is placed. The border (5) marks an iso-contour surface of the stray field at a specified magnetic field strength. The platform (1) therefore forms a natural barrier that prevents people or objects being exposed to magnetic field strengths that are too high. To this end provision is additionally made, in accordance with the invention, for a step (15) for the marking of an iso-contour surface of a stray magnetic field of an MR device (2) at a specified magnetic field to be used.