IBM 1620 invalid character symbol
Ian Clifton via Unicode
unicode at unicode.org
Tue Sep 26 11:23:56 CDT 2017
William Overington wrote:
> A digit with a bar over the top is used to express the common logarithm of a number that is both greater
> than zero and also less than one.
Gosh, I’d forgotten that usage, although I now remember being taught it at school.
Another use of over bar for negative numbers is in crystallography—I believe the motivation is that it’s useful
to have a very compact notation for (often space separated triples of) small integers of either sign.
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