Posting this here as a result from a question that came in under Supporting Documentation (check that post out as well for some additional info!):

Signal Calibration: This pertains to the secondary and tertiary devices that convert the meter reads into flow volumes. Specifically, it measures the alignment of flow range conversion with signal span output (typically 4-20mA DC) and SCADA output. The image below helps illustrate the difference in volumetric meter accuracy testing and signal calibration: