HP 5501A Operating And Service Manual page 96

Upon command from the system controller (Figure 3-3), the contents of the 10760A Counters
are sampled. This can be accomplished independently or simultaneously on the X- and Y-axis.
The 10755A Compensation Interface i s used with either the 10756A Manual Compensator or the
5510A Opt 010 Automatic Compensator. In typical installations, the choice of manual or auto-
matic compensation is determined by the stability of the ambient environment.