Comparison of tests of GR in the plane of mass and potential, adapted from Psaltis (2004). Black: terrestrial laboratories, Mercury’s precession, light deflection, and Shapiro delay in the Solar System, the Hulse-Taylor pulsar, the LIGO detections, the relativistic Kα lines, and the M 87 EHT observation. LISA signals will probe the grey rectangular region. This work, using S2, is marked in blue.