Tracking of Uranus with RxA3i and the fives method was performed for about 2 hours between HST 02:30 and 04:25. Uranus moved from (az,el) = (121,39) to (154,57), and the empirical correction was disabled throughout.

At azimuths 125 and 141 the race defect reveals itself as +ve & -ve excursions in the azimuth residuals. The green line is the current empirical correction.

The defect amplitude (peak-to-peak) at (az,el)=(125,39) is 5.6", while that at (141,49) is 3.3", giving amplitudes at the horizon of 7.2" and 5.0", respectively, and therefore a mean of 6.1", cf ~7.0" when last estimated on 03 June. The error on the new estimate however does not justify changing the amplitude of the correction at this time, although monitoring will continue.