SUMMARY
The low amplitude of the c.b. defect as measured earlier is confirmed.

A new record low amplitude (6.5") was deduced from the measures on 990427 . A new measure, at a different azimuth (if that means anything !?) was made last night. Mars was tracked using repeated RxA3I fivepoints, with the empirical corrections disabled, from :

• (az,el) = (235/40) at 02:31 HST to (246/27) at 03:33.

The elevation residuals are well behaved, with an rms scatter of 0.5", although the value of the seeing as measured by the SAO phase monitor was about 0.2" through this period.

The azimuth residuals show the extent of the defect at this time.

Accounting for the baseline slope in the azimuth residuals the peak-to-peak excursions amount to 6.4", and allowing for the lag of the logging process behind the center of the fivepoints, the event occurs at (az,el) = (240.1, 34.5). Given the structure in the profile, this agrees quite well with TEL_EMPIRICAL, which has this event centred at azimuth 240.4 degrees.

The observed error then corresponds to an error at the horizon of 6.4"/cos(34.5) = 7.8", reasonably similar to the estimate of 6.5" made earlier .

The new data are added to the collection .