The ABBITZ Model 311A is a differential pressure indicator used to measure pressure, fluid flow, or liquid level. It works by detecting pressure differences from devices like orifice plates or from changes in liquid level within a vessel. The unit features a pointer that moves across a 270-degree scale, with precise internal components that allow easy adjustment of range and zero settings. Additional calibration options are available for fine-tuning performance. It is also designed as a direct replacement for the Barton Model 200A indicator.