Top left: calibrated chromatic phases of our UT baseline measurements of HD 100546. The 34 m baselines is plotted with dotted and 41 m baselines with full lines. The 70 m baseline presented in Leinert et al. (2004) is plotted with the dashed line. A linear, atmospheric term has been subtracted from the shown phases. Also shown are the zero phases, as predicted from our point symmetric model. The grey area represents the ±3° tolerance for deviation from zero. Top right: calibrated chromatic phases of our AT baseline measurement of HD 100546 taken on 2006 February 16. The tolerance for deviation from zero (point symmetric model) is ±5° and indicated in grey. Bottom left: differences between the measured phases of two point-source calibrators (no asymmetry) at different airmasses, to illustrate the level of atmospheric contributions of our UT measurements. Bottom right: as above, for our AT measurements.