Flow straighteners eliminate rotation of fluids and steady velocity profile of fluid flow, enable to shorten length of inlet piping in front of primary element, especially behind adapting pipes not stated in the standard. Individual types of flow straighteners differs by construction design ( „Zanker" – perforated tile+bundle of channels, „Sprenkle" – 3 perforated tiles, bundle of pipes, AMCA – seam of channels of square sections, „Etoile" – 8 radial lamellas arranged in the star-shape) and its use. Use of flow straightener helps to achieve higher stability and accuracy of measured flow.