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In page Numeral system:

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The unary notation can be abbreviated by introducing different symbols for certain new values. Very commonly,[citation needed] these values are powers of 10; so for instance, if / stands for one, − for ten and + for 100, then the number 304 can be compactly represented as +++ //// and the number 123 as + − − /// without using a zero. This is called sign-value notation. The ancient Egyptian numeral system was of this type, and the Roman numeral system was a modification of this idea.