Notes. Each of the 30-day Euclid windows occurs within a corresponding 72-day observing window for Roman. The S/N and parallax criteria required for joint detection are discussed in the main text. Columns (3)-(6) show the effect of introducing different combinations of event selection criteria on the detection rate. Where no parallax or finite source measurement is possible (“S/N only”), only a statistical order-of-magnitude FFP mass measurement is possible. Where either parallax or finite source size is measured, the three-way microlens degeneracy is partially broken resulting in much improved statistical mass determinations (around a factor of 2 uncertainty). When both parallax and finite source are measured (“All constraints”), the microlens degeneracy is fully lifted and a direct mass measurement is possible. The ability of Roman and Euclid to work together to measure parallax allows a huge improvement in the fraction of events (85–90%) where the parameter degeneracy is partly or fully broken.