Illustration of the geometry of X1822-37. The figure is to scale except for the size of the region in the bulge where the O viii, Ne ix, Ne x, Mg xi, Mg xii, and Si xiv lines originate (white circle). The black-coloured arc at the outer radius of the disc indicates where the outer disc is the highest, which is the location of the bulge. The dashed and dotted circumferences on the disc indicate where the O vii and Fe i-Fe xv lines are produced, respectively.