Explanatory notes
… (rivers, waterways, etc.) and through closed conduits (piping, etc.). Some flowmeters use the principle of the fluid meters of heading 90.28 (turbine‑type, piston‑type, etc.), but the majority are based on the … . These comprise essentially : (i) a primary device (e.g., Pitot or Venturi tube, simple diaphragm, orifice plates, …