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.
> https://en.wikipedia.org/wiki/Common_logarithm 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. -- Ian Clifton
