Plots of closure phases at the X band for source 0552+398 as a function of GMST for two triangles, (a) GILCREEK–NYALES20–WETTZELL and (b) FORTLEZA–NYALES20–WETTZELL. See Figure 1 for a description of the plot design. The patterns were stable and were only slightly evolved over more than 20 yr in 332 sessions for the first triangle and in 463 sessions for the second.