Rotameters use a float inside a transparent vertical tube to determine the flow rate. Our products have limitations. It consists of a tapered tube, typically made of glass, with a float inside that is pushed up by flow and pulled down by gravity. These can be only used in vertical position with upward flow and cannot be used in fluids that contain solids. This is a variable-area, constant-head, rate-of-flow volume meter in which the fluid flows upward through a tapered tube, lifting a shaped weight to a position where upward fluid force just balances its weight. This can accurately determine flows of low velocity. It is used only in small pipes with relatively low flow. These are very simple and versatile and can be used with a wide variety of liquids and gases over wide ranges of flow rates. The advantage of rotameters are relatively simple device that can be mass manufactured out of cheap materials, allowing for widespread use in places such as third world countries.