SUMMARY
The transit tracking data taken since the discovery data have invariably been taken with SCUBA. The azimuth of symmetry of the error function has apparently drifted away from 180 degrees at discovery to as much as 185 degrees in July. The possibility that the error and/or the drift are related to the position of SCUBA outside the receiver cabin is tested here by repeating the transit tracking experiment with RxA.

These RxA results appear similar in all respects to recent SCUBA data.

The 'transit' problem was noticed first in April . A correction was installed on 16 May, but recent checks in May, June and twice in July, and once again in August have been inconclusive for various reasons.

Uranus was tracked with RxA using the icl fives procedure from (az,el) = (158,51) at 21:30 to (198,52) at HST 23:10 with a transit at elevation 54 degrees.

• The noise in the measures is of order 0.8" to 0.9" prior to transit, which is exactly the seeing recorded during that period, becoming slightly worse during the second half of the experiment.

• The ~4" step is clearly seen. The data were acquired with the s-correction activated erroneously, but have been corrected for this presentation.

• The data do not appear symmetric about azimuth 180 but about 184. (Click on the image for a larger one).

• The next test must be to perform transit tracking through the north : the azimuth of symmetry in the north should throw further light on this problem.