Residuals of optical and radio phase with respect to a BIM model. Left: best-fitting BIM to 2009 Iqueye data (n = 2.437). Right: best-fitting BIM to 2008−2009 Aqueye and Iqueye data (n = 2.476). Optical residuals are plotted as red data points clustered at the time of optical observations, while Jodrell Bank residuals (over the same interval of time) are represented by a gray line crossed by error bars at epoch dates of JBE. Insets: zoom of average optical phase residuals during observation nights with 1σ error bars. The scales of the y-axis in the insets are very different.