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I want to display the symbols commonly known as h and h-bar. This is for Safari and iOS. What do I enter into my html?

If there is a table of such things somewhere, a reference to it would be great. Thanks!

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You're looking for a list of unicode characters and an explanation of how to use them. Unicode characters should work in any browser regardless of platform.

The ℏ is written as ℏ and ℎ as ℎ in a html document.

If you're representing complex equations you might get on better with LATEX

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Regarding information about such things in general, the Unicode standard is authoritative in matters of character codes. But it does not prescribe the use of characters. Various sources need to be consulted; in matters of mathematical and physical notations, you can consult the ISO 80000 series of standards (available from standards organizations for rather high prices).

The Planck constant can be viewed as letter h in italic, but the non-normative well-written advisory document Unicode in XML and other Markup Languages says: “to indicate Planck's constant one should use U+210E and not <i>h</i>” (the logic behind this is not simple, but logical). For the reduced Planck constant, there really is no choice. So use the characters U+210E PLANCK CONSTANT and U+210F PLANCK CONSTANT OVER TWO PI. The way to enter them depends on the authoring context.

In modern authoring, you should be using a Unicode-enabled editor and should be able to insert these characters directly. Failing this, the character references mentioned by toomanyairmiles can be used.

Then there’s the character problem. These special characters have limited support in fonts. You should probably analyze their availability and suggest a list of fonts in CSS, as outlined in my Guide to using special characters in HTML.

Note that the reduced Planck constant character has varying shapes (glyphs), with either horizontal or slanted stroke over the letter h. The glyph in the relevant Unicode chart has a slanted stroke. This is not normative but suggestive, and it makes it clear that the character is different from h with stroke (ħ, a letter used in some natural languages).

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  • You raise a very good point about font support, and in the fractured world of mobile that may be a very big issue. Thing is I'm not clear if you think my answer is right or wrong, or if there is a better approach?
    – toomanyairmiles
    May 28, 2012 at 19:28
  • @toomanyairmiles, your answer is correct, but instead of character references, real characters can be used, too, and additional markup may be needed (to enclose the characters into elements, so that their font can be set as different from normal copy text font, if needed).
    – Jukka K. Korpela
    May 29, 2012 at 4:50
  • Checking the characters on my Android, I saw both of them as small boxes, like I sort-of expected. So if only the Planck constant is needed, using <i>h</i> is more practical than the recommendation. If you also need the reduced Planck constant, you could consider using an embedded font, or using MathJax (which renders LaTeX notations with client-side JavaScript).
    – Jukka K. Korpela
    May 29, 2012 at 4:54

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