The tracking accuracy is
dependent upon the time resolution of the PDP-encoder interface, which is
100Hz, and the angular speed of a source across the sky. This latter reaches
a maximum for a source transiting close to the zenith, and to track
accurately through the zenith itself would require infinitely fast
computing. A general limit for tracking is currently 85
elevation.
Transit here occurs at a rate of about 500
/sec, implying a
pointing
resolution, in azimuth, of 5
. This falls to 2
at
75
elevation, and to 1
at 65
elevation, or to 1
at
85
elevation and 20
from transit. This ought to define our
pointing zone of avoidance, but pointing is done in this region.
We do not ascribe errors from this source but note that data from this zone
be treated with caution.
The resolution of the track model causes residual errors where the track
changes on scales smaller than the resolution. As shown later, 1
resolution models left considerable residuals in this regard, but our newer
models have reduced this to perhaps 0.1
rms.