The vast majority of engineering computations require a complex set of mathematical operations such as logarithms and trigonometric functions. Functions are predefined formulas that simplify manual entry and allows us to carry out calculations that would otherwise be impossible. Excel and other mainstream spreadsheet apps have an extensive library of built-in functions. For example, we can use the SUM function to total all the values in a column or use the MAX function to find the biggest number in a range of cells. However, functions can do a lot more than just math. They can look up data in another location, calculate cells only if they meet a specific criteria and combine the contents of two or more cells.