seven-segment display

Most calculators use a seven-segment display to show both input and output numbers. Here is Champernowne’s constant $C_{10}$ to 9 decimal places in a seven-segment display:

Technically, the space for the decimal point counts as a segment, so for each place value there are actually eight segments. Generally, calculator manufacturers prefer the base 10 pandigital number 1234567980 as a demo number for the calculator packaging.

Sometimes wear and tear can cause a segment to not light up or darken properly; this can occasionally lead to confusion between digits. The simplest way to test for this is to input $8\times \frac{{10}^x-1}{9}$, where $x$ is the the number of decimal place values available on the display (that is, a bunch of 8s). At various times in the past some manufacturers have developed variants of the glyphs for the digits to make it more obvious when a segment has burnt out, such as a 0 that looks like a lowercase O, or a 6 that looks like a lowercase B. Given that many scientific calculators offer the option of doing calculations in hexadecimal, the latter option is not acceptable for such calculators. The 7 on Sharp-brand calculators uses the upper left vertical segment.