Seven segment displays are widely used in lcd calculator displays. They consist of vertical and horizontal bars that be either light, presenting no contrast with the background, or dark, showing up against the background, depending on whether or not a voltage is applied.
To display a number a sequence of 0's and 1's is sent along the data cable to the display. In all, the seven segment display allows
different combinations of light and dark bars, though not all of these are used.