Closure phases vs. time for three independent VLBI triangles. Each data point denotes a closure phase measurement averaged over one scan of six minutes; error bars correspond to 1σ errors. Dotted lines indicate weighted averages of all data points, dashed lines represent the corresponding standard errors of mean. Average phase values are noted in each diagram. Phases for the triangle EF-PB-PV are extracted from Stokes I data, phases for the other triangles from LL data.