According to OSHA and NIOSH sampling and analytical guides, establishing the correct volume of air through a filter or sorbent media is essential for a more accurate calculation of concentration. The flow rate of an air sampler is calibrated with the sampling media in line using a field flow calibrator. Some air samplers have a built in calibrator or the use of dry piston prover field calibrator. The flow should be checked before and after each sample. If the volumetric flow uncertainty is known, concentrations can be ultimately presented as data in lower and upper confidence limits. This will provide better data for OSHA compliance and engineering controls. Many of the calibrators come in reading modes of single, continuous, and burst.