Plots of closure amplitudes at the X band for source 0642+449 as a function of GMST for two quadrangles, (a) KOKEE–NYALES20–TSUKUB32–WETTZELL and (b) KOKEE–NYALES20–TSUKUB32–WESTFORD. See Figure 5 for a description of the plot design. Its structure has dramatically evolved several times. The largest magnitude of closure amplitude in plot a is −4, so that the ratio of the observed amplitudes of the four baselines was less than e⁻⁴ (∼0.04). The closure amplitude patterns change very rapidly with respect to GMST in plot b. A very extended structure is detected.