SUMMARY
These data are a continuation of the effort to reveal the extent and size of the elevation pointing errors induced by the reversal of direction in elevation that becomes so apparent during transit tracking (see the reports during April 2000 ).

These data were taken on UT20000421 when conditions were not good enough for the scheduled program. Following pointing and focussing on 3c273 at HST 21:00, map16 experiments, typically lasting n_integrations=20, or 15mins, were executed on 3c279 and 3c273 in turn. The data are shown below in their confusing entirety :

The 260 individual azimuth data have an rms scatter in azimuth of 1.0", which was approximately the recorded value of the seeing during the experiment. The elevation data are of greater interest here and the analysis below focusses on them only. The experiment was designed to reveal the values of two possible quantities :

1. the instantaneous pointing shift resulting from moving the telescope
2. the relaxation of the telescope in the minutes after the slew.

The instantaneous pointing error
To better illustrate the first of these, we plot below only those elevation residuals measured immediately before and after each slew.

del -vs- azimuth	del -vs- elevation	del -vs- elevation (detail)

The leftmost plot shows that slewing from 3c273 to 3c279 (from the 2^nd of the pairs of '3's to the 1^st of the pairs of '9's) consistently required an increase in del : for the 6 such motions we have observed here the change in del is 2.3"+2.6", although without the very large first jump the change is 1.3+0.4". Going from 3c279 to 3c273 yields similarly -0.5+2.4". All the 3-9 slews were upward in elevation and all the 9-3 slews were down, so a pattern may be present, although this would be in conflict with the analyses of other pointing datasets (see the reports of 2000 04 08 , and 2000 04 25 .)

Relaxation
If some relaxation of the antenna occurs in the minutes following slews then the map16 data should be able to temporally resolve it. We present below the elevation residuals from each map in turn.

#107	#108	#109	#110	#111	#112	#113	#114	#115	#116	#117	#118
3c279	3c273	3c279	3c273	3c279	3c273	3c279	3c273	3c279	3c273	3c279	3c273

The occasional plot looks suggestive of the effect we seek, but overall there appears little pattern.

Conclusions

1. Some small systematic pointing shift associated with the direction of elevation slew may be present, but this is in conflict with other, more extensive, analyses.
2. There is no evidence for any elevation pointing relaxation in the 10 minutes or so following slews.