Arguments:

tele:      A rotator.telescope object describing the observatory at
           which the instrument is situated.
tgt:       A rotator.target object representing the target field
dt:        The interval at which tracking adjustments should be made,
           in seconds.
low:       The lower limit of allowed motion, a rotator.angle object.
high:      The upper limit of allowed motion, a rotator.angle object.
port:      A serial.Serial object for communication with the hardware.
stop:      A threading.Event object used to terminate the tracking
           loop.
lockedOn:  A threading.Event object used to indicate tracking within
           tolerances.
logger:    A logging.Logger instance used to output information.
logData:   Boolean to indicate whether tracking status information
           should be logged to the file 'dicstrack.log'. Default False.

Overrides: threading.Thread.__init__

Overrides: threading.Thread.run

Based on the currently set target and telescope calculates the
required rotator position for the UTC given as a datetime.datetime
object.

DAzLE will mount on VLT UT3 Nasmyth platform 'A', which is on the
LEFT hand side when looking in the direction in which the telescope
if pointing.  For the left hand Nasmyth platform the position angle
of the sky image on the detector with the rotator at zero degrees is
equal to parallactic angle + zenith distance + 180 degrees.  The
required rotator position is therefore requested PA - parallactic angle
- zenith distance - 180degrees, appropriately normalised into -180 to
+180.