\subsection{Gain Tracking Scaler}

MX scaler driver to control MX gain tracking scalers.
Gain tracking scalers are pseudoscalers that rescale
their reported number of counts to go up and down when
an associated amplifier changes its gain.

For example, suppose that the real scaler was reading
1745 counts, the amplifier was set to $10^{8}$ gain and the
gain tracking scale factor was $10^{10}$.  Then, the gain
tracking scaler would report a value of 174500 counts.
If the amplifier gain was changed to $10^{9}$, then the gain
tracking scaler would report a value of 17450 counts.

Gain tracking scalers are intended to be used in
combination with autoscaling scalers, so that when the
autoscaling scaler changes the gain of the amplifier,
the values reported by gain tracking scalers will change
to match.
