The figure shows the display on a calculator screen with annotations added to explain some of the features. The top row of the screen contains the letter D (white text on black) in the centre, and the word ‘math’ with an upward pointing arrowhead towards the right end, and these are annotated with ‘display indicators’. The middle row of the screen has the mathematical text 1 add 2 at the left-hand side, annotated with ‘input’. The bottom row has the mathematical text 3 at the right-hand side, annotated with ‘output’.