Example of a unary fit for a five-minute exposure on Sgr A* from April 22, 2019, 06:39:55. Top: phase Φ as a function of projected baseline vector u for the s-polarisation channel. Per baseline, eight spectral channels were included here. The black line is a unary model, which yields the offset from the interferometer pointing position to ΔRA = 322 ± 9 μas and ΔDec = 301 ± 8 μas (formal fit errors). Bottom: the visibility modulus for the same data is constant and close to unity, consistent with the choice of fitting a single point source.