mock-up of a basic calculator

This mock-up of a basic calculator is realistic in that it has almost every function one can expect on a typical basic calculator. The layout will of course be different on an actual calculator. A calculator shaped like, say, a credit card will have more columns of buttons than rows.

A basic calculator can be counted on to have buttons for the basic arithmetic operations (addition, subtraction, multiplication and division). A button for square root is sometimes provided, its operation usually being “postfix”. The percentage key, when provided, does not always behave in a standard way. For example, on some calculators, a 15% tip on a meal costing $\$42.54$ might be computed as $[4][2][.][5][4][+][1][5][\%][=]$.