Hi, My name is Andy im a new user here. Im having a bit of trouble deriving the difference between the Francis Formula and the Torricelli Formula. I have the following question to work on as part of many which could be covered in an exam shortly: Provide an expression for the Francis Formula used for calculating flow over a weir, explaining any improvement over the simple Torricelli derived formula and a reliance on the concept of contractions to a weir. I am comfortable using each of the formulas and solving problems based on them but I am not too sure on how they relate to each other and the benefits of using one or the other. Any advice would be much appreciated!