The same scale lets you track the action during exposure and even measure the amplitude and direction of the drift. The dynamic range is the range of usable input energies and is very large on this model. The gain is incredibly high which means it will oscillate but it will also lock on very tightly. The stability is better than the spec of a 20th of a wave when care is taken to generate large clean smooth fringes. The sensors are simple , rugged photodiodes in a balanced differential pair and the bimorph is damped and rigidly mounted.
Drift is very low without feedback and essentially zero after a lock is made.
Monitoring via a strip chart recorder is made convenient from a BNC output connector. It is only difficult for the first time or two and is usually quite simple to accomplish, requiring at times a little ingenuity and always some patience to generate fringes. The hardware is fairly rugged and laser grade dielectrics or prisms may be used by simply gluing them over the existing mirror. First timers are advised to experiment with their tables in the manner previously described to discover not only how to use the devices but to determine what is moving and what is not in any set up. Since the task is usually to compensate for table growth a separate laser and optical paths running parallel to the holographic set up with one shared mirror may work for you.