Re: Questions about proposed characters

From: Markus Kuhn (
Date: Sun May 30 1999 - 06:17:00 EDT

Curtis Clark wrote on 1999-05-30 04:15 UTC:
> There are also two symbols that could be made with combining diacritics,
> one well and one not so well. The first is X-BAR, the symbol for arithmetic
> mean. I imagine this has already been settled; could someone point me to a
> web reference?
> The second is a symbol that might be called V-DOT, Latin capital letter V
> with dot above, that is used by some physiologists to indicate the volume
> of a gas used or produced. I imagine that U+0307 COMBINING DOT ABOVE would
> normally be sized to fit over a lower case letter, so that V-DOT would not
> look right by using it. But I'm unclear on the implementation of the
> combining diacritics. Has V-DOT been proposed? What is the working
> philosophy on things like this?

The X-BAR and V-DOT is very unlikely to be included:

Unicode combining characters are supposed to fit over every character,
just like the combining characters in TeX do. High-quality fonts contain
information about the coordinates at which combining characters are to
be placed around every character. Just like TeX uses combining
characters (e.g., \" to put diareses on the following character) to
provide mathematicians and scientists with dots, tildes, bars, hats,
etc. over absolutely EVERY character, Unicode also expects people
involved in typesetting scientific texts to use combining characters.
ISO 10646-1 Level 1 & 2 (i.e., no combining characters) are not intended
to be suitable for scientific typesetting. Scientists require a lot of
freedom in their notations and are unlikely to become happy with just
the two precomposed characters that you suggest. I have also used both
V-BAR (average volume) and X-DOT (first derivative of x over time) before
for instance.

The other characters that you propose sound more reasonable to add,
as they are not already in ISO 10646-1 Level 3: Would it possible for you
to provide as exhibits the scanned pages from a few textbooks in the
field where these symbols are used in context, together with a
bibliographic reference? Even better would be quotations of where these
symbols are defined. It might however already be too late to get these
into Unicode 3.0, as I understand that this repertoire has already been


Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
Email: mkuhn at,  WWW: <>

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