The servo velocity demands for the telescope drive depend on the distance of the telescope to the source it has to go to. There are three regimes of velocity control ensuring that for small position error (PE) the correction is critically damped, whereas for larger distances the velocity increases with increasing distance (but within the physical specification of the drive):
where k and k 
are linear gains and k is the integrator gain.
The relevant Task Common variables are TGLH, TGLD, HGI and DGI. These
are likely to need resetting after any alteration to the telescope
drives. The objective is to obtain parameter values for which a critically
damped offset with minimal fluctuations is realised when tracking.
There is a certain art involved in assessing the correct values, the telescope
performance being judged from the TV, position error displays and the
velocity demand display. A basic requirement is, of course,
that the telescope should track with approximately zero position error.
The autoguider errors are logged by the Telescope Control Software and the
servo constants are adjusted until the guiding errors are minimised.
If any of the DACs on the axes get changed, then the parameters HDAC and/or
DDAC will need to be checked.