in any of the combined images. The weighted mean of those values is then the final measurement of separation (and PA) of that epoch, and the standard deviation is the precision of that measurement. We use the larger error values in Table 2 for the absolute errors. Since the calibration binary HIP 73357 has changed its PA significantly since 1991.25, the calibration errors in PA are relatively large, so that they overwhelm real measurement errors.

![image](PArev.ps){width="120mm"}

We correct the separation measured in pixels and the PA measured for GQ Lup and its companion with the calibration values given in Table 1. In Table 2, we list the values for separation and PA between GQ Lup A and its companion. In Figs. 1 & 2, we plot the PA and separations versus time, as observed and listed in Table 2. The precision of the measurements decrease slightly from 2005 to 2006 and are worst in 2007, where we have strong reflection effects and a strong waffle structure (bad seeing, large FWHM). This decrease is at least partly due to the fact that the error in the astrometric calibration binary from its possible orbital motion since 1991.25 (Hipparcos) increases with time. The 