The Model ST51A flowmeter is an insertion-style instrument designed for use in pipe diameters larger than 2 in. (51 mm); it is optimized for flow measurement of air, compressed air, nitrogen, natural gas, digester gas and all other biogases. The ST75A flowmeter is an inline-style instrument designed for use in pipe diameters from 0.25 to 2 in. (6 to 51 mm); it is designed for applications in air, all inert gases, natural gas and other hydrocarbon gases. They were independently evaluated by functional safety experts Exida and found to meet SIL 1 compliance.