The angular size, distribution and position uncertainties of the maser components making up the boxed features A–D around S Per in Fig. 8, as measured in 1994 (upper and middle plots, circles) and the features in A as measured in 1999 (lower plot, triangles). The same velocity colour scheme is used. Region A contains 6 features in 1994 and 5 in 1999; the other regions contain 2 features, as can be seen from the spectral peaks in Fig. 11. The diameter of each symbol is 10% of s_υ. The black lines join the components in velocity order. The position uncertainties are shown.