"Flowmeter Tube: Borosilicate Glass Accuracy: +/- 2% of full scale value. Free standing or wall mounted flowmeter with 300mm scale variable area tube. Supplied with tubing connectors and foam rubber disc which can be fitted to top of flowmeter to form an air tight seal when a sampling head is pressed onto it. This is invaluable when setting flow rates. Due to the large scale of this flowmeter, accuracy is excellent and it is often used as a `master` flowmeter when calibrated to UKAS standards "