M 87^* (u, v) coverage (colored points) in band 3 (top panels) and band 2 (bottom panels) for observations on 2018 April 21 (left panels) and April 25 (right panels), overlaid on the low-band (u, v) coverage for 2017 April 11 (gray points). The dashed circles show baseline lengths corresponding to fringe spacings of 25 and 50 μas respectively. The (u, v) coverage in band 1 and band 4 is comparable to that in band 2 and band 3, respectively.