SUMMARY
The new pointing catalog was used in earnest for the first time during a dedicated pointing run. Its performance, and that of the pointing model, seems fine.

36 blazars, mainly the brighter ones and mainly those with entries in the old pointing catalog , were observed in two spells at the start and end of an unusual 7 hour shift in the middle of the night. Raw residuals in (daz,del) were (0.0+1.5, -0.4+2.1). Throughout the night additional pointing measures were made of Mars, Uranus, Saturn, Venus, CRL618 and NGC2071IR, and this total of 50 measures gave (0.0+1.5, -0.5+2.0) and showed essentially the same structures described later. These 50 raw data are shown below :

The azimuth residuals are pleasingly random as a function of azimuth (upper left) while showing a slight turndown when plotted against elevation (upper centre). The elevation residuals appear random as a function of elevation (centre), but show a bow-shaped systematic trend when plotted against azimuth (centre left). Neither of the systematics has a source within the 7 parameter telescope model . Nonetheless, we can use the data to improve the model if possible. All 50 data are used, and yield rms scatters in (daz,del) of (1.2,1.7) as shown below :

The azimuth residual turndown has gone and the azimuth residuals are almost ideally random, while the elevation residuals' bow has almost flattened out. The changes to the parameters and their new values are shown below :

 PT991115_18.DAT                                                                 
 model #   492
 SCUBA
 No. of points  =  50

  N           OLD    FIXED=1      +          +            NEW

  1          11.2       0        0.0       -0.9          10.3
  2          17.8       0        0.0       -0.7          17.1
  3          50.9       0        0.0        7.9          58.8
  4         158.8       0        0.0       11.0         169.8
  5   229 55 26.1       0        0.0        8.6   229 55 34.7
  6   351 19 21.5       0        0.0       -0.9   351 19 20.6
  7         -13.1       0        0.0        0.5         -12.6
  8           0.0       1        0.0        0.0           0.0
  9           0.0       1        0.0        0.0           0.0
 daz =   0.0 +-  1.2     del =   0.0 +-  1.7     vec =   1.8 +-  1.0

Even if these adjustments to the pointing model are not the best way to counter the observed systematics, particularly the elevation 'bow', the complete coverage in (az,el) space of the current dataset ensure that future spurious systematics resulting from the new model will be minimal.

Conclusion

• The old model was working well.
• The use of the new (J2000) coordinates has not adversely affected the model.
• The coordinates of blazars, non-blazars, and planets seem compatible.
• Minor adjustments to the pointing model have been made.
• Expected performance : given the vagaries of pointing I think it is safest to say that the model is still fairly represented by rms scatters of 1.5" in each coordinate.
• The new model was installed at 13:40 HST 16 Nov 1999.
• Given the impossibility of fully checking every entry in the new pointing catalog on the sky, I hereby declare the new catalog operational. Please use it and report any inconsistencies that remain. Thanks.
  It is available at
            observe:[imc]point2000.cat ,
  as well as within
            observe:[gms]m99b.cat (etc).