By following the change in absolute pressure above a permeation device, calibration of such sources can be performed in substantially less than one hundredth the time required using conventional gravimetric procedures. The sensitivity of the Brookhaven calibration procedure is achieved by combining high resolution pressure and temperature measuring instruments with newly designed permeation wafer devices giving low total volume when connected to the pressure measuring device. Using Brookhaven low (<20 nl/min at 30°C) and ultra-low (<1 nl/min) calibrated permeation devices, the inaccuracies and expense associated with the use of exponential dilution flasks and large quantities of diluent “zero” gas for providing part-per-billion calibration gases are reduced markedly. In addition, controlled flow rates of noncondensable gases such as carbon monoxide and methane can be provided at microlitre-per-minute rates using Brookhaven porous glass diffusion devices.