In this document, the authors provide an overview of the gas flow calibration service and the procedures for customers to submit their flowmeters to the National Institute of Standards and Technology (NIST) for calibration. They also document the flow calculation algorithms and uncertainties of the WGFS.

This document discusses the procedures for submitting a flow meter for calibration, gives the readily available pipe sizes and flanges suitable for flow meter calibration, documents the format of a standard NIST calibration report, and states the normal range of data collected for a calibration. In addition, this document describes the theory, principle of operation, and uncertainty of the 26 m3 PVTt primary flow standard covering the flow range from 200 L/min to 77000 L/min. Details concerning the two smaller PVTt flow standards can be found in the following reference.