a dialog box. An on-line formula calculator hosted on a web site. It can also be entered on the command line of a programming language. Related software packages Although they are not calculators in themselves, because they have a much broader feature set, many software tools have a formula-calculation capability, in that a formula can be typed in and evaluated. These include: Spreadsheets, where a formula can be entered to calculate a cell’s content. Databases, where a formula can be used to define the value of a calculated field in a record. Declarative and imperative tools Button-operated calculators are imperative, because the user must provide details of how the calculation has to be performed. On the other hand, formula calculators are more declarative, because the entered formula specifies what to do, and the user does not have to provide any details of the step-by-step order in which the calculation has to be performed. Declarative solutions are easier to understand than imperative solutions, and so there has been a long-term trend from imperative to declarative methods. Formula calculators are part of this trend. Many software tools for the general user, such as spreadsheets, are declarative. Formula calculators are examples of such tools. Hybrid calculators There are hybrid calculators that combine typed-in formulae and button-operated calculation. For example: Calculations can be entered entirely from the keyboard, or operations can be applied to typed-in numbers or formulas using buttons, in the same calculator. Formulas can be constructed using buttons, rather than being entered from the keyboard. Formula copies of button-operated calculations can be created, saved and re-loaded for application to different numbers. See also Software calculator Comparison of software calculators Calculator Calculator input methods Programmable calculator Scientific calculator References Calculators Office equipment Mathematical notation