The topic of seven-segment display character representations revolves around the various shapes of numerical digits, letters, and punctuation devisable on seven-segment displays. Such representation of characters is not standardized by any relevant entity (e.g. ISO, IEEE or IEC). Unicode provides encoding codepoint for segmented digits in Unicode 13.0 in Symbols for Legacy Computing block. Digit Two basic conventions are in common use for some Arabic numerals: display segment A is optional for digit 6 (/), segment F for 7 (/), and segment D for 9 (/). Although EF () could also be used to represent digit 1, this seems to be rarely done if ever. CDEG () is occasionally encountered on older calculators to represent 0. In Unicode 13.0, 10 codepoints had been given for segmented digits 0–9 in the Symbols for Legacy Computing block: Alphabet In addition to the ten digits, seven-segment displays can be used to show most letters of the Latin, Cyrillic and Greek alphabets including punctuation. One such special case is the display of the letters A–F when denoting the hexadecimal values (digits) 10–15. These are needed on some scientific calculators, and are used with some testing displays on electronic equipment. Although there is no official standard, today most devices displaying hex digits use the unique forms shown to the right: uppercase A, lowercase b, uppercase C, lowercase d, uppercase E and F. To avoid ambiguity between the digit 6 and the letter b the digit 6 is displayed with segment A lit. However, this modern scheme was not always followed in the past, and various other schemes could be found as well: The Texas Instruments seven-segment display decoder chips 7446/7447/7448/7449 and 74246/74247/74248/74249 and the Siemens FLH551-7448/555-8448 chips used truncated versions of "2", "3", "4", "5" and "6" for digits A–G. Digit F (1111 binary) was blank. Soviet programmable calculators like the Б3-34 instead used the symbols "−", "L", "C", "Г", "E", and " " (space) to display hexadecimal numbers above nine. (The Б3-34 character set allowed for a cross-alphabet display of the English word "Error" as either EГГ0Г or 3ГГ0Г, depending on the error, in all-numeric form during error messages.) Not all 7-segment decoders were suitable to display digits above nine at all. For comparison, the National Semiconductor MM74C912 displayed "o" for A and B, "−" for C, D and E, F, and blank for G. The CD4511 even just displayed blanks. The Magic Black