Report to the JCMT Board; April 2006
(for the 6 month period ending 31 January 2006)

Introduction
The period started with a relative novelty : a central bearing load adjustment, and a recovery of the pointing model using - for the first time in several years - a front-end other than SCUBA. All went nominally.

All-sky pointing
The pointing performance was recovered satisfactorily, although with a suspicion that the additional time required to acquire pointing data with a heterodyne front-end leads to increased time- (i.e. refraction- ) dependent errors in elevation: formal rms scatters in (azimuth,elevation) following the model installation were (1.5", 2.4"). They remained approximately at that level thereafter.

Inclinometry
Measurements of the antenna track profile are made every couple of weeks or so, and have shown only minor changes during the past 6 months; the most concern being generated in August by ~2" changes in the track profile seen in data taken when the ambient temperature was particularly high (almost 10degC). Subsequent inclinometry and pointing showed that any impact upon pointing was being accommodated by the models.

Transit step and central bearing race defect
Characterization of both these effects demands the highest possible resolution in azimuth and time, previously provided best by SCUBA in jiggle-map mode than by the heterodyne receivers in continuum-pointing mode. Neither phenomenon was checked during the reporting period.

Temperature corrections
Algorithms that correct the pointing and focus for changes in the ambient or structural temperatures are checked each month. Minor updates (tweaks) were made during the reporting period in order to maintain best performance.