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When reading an article in Der Spiegel I came across a symbol that looks like a slashed zero. However, a slashed zero, which is just a fancy way of writing down a zero, does not seem particularly meaningful to me at the place where it appears in the article.

Please have a look at the below screenshot: "Ø" appears in two places at the very bottom of the screenshot. What does the symbol mean?

enter image description here

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    Durchschnitt, average. – Robert Oct 31 '16 at 20:37
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    I'm a bit surprised, that the German Wikipedia article (linked by Stephie) has no English counterpart, even though it states a mathematical sign. Has anybody objections to add the "typography" tag? – guidot Oct 31 '16 at 21:18
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    @guidot In English, it's only used to mean diameter; never average. That usage is detailed in the page on Diameter. In my experience, it's only used in engineering, so I wouldn't even call it a mathematical symbol. In any case, it seems quite common for symbols not to have English wikipedia pages: rather the page is about the concept denoted by the symbol. After all, it's difficult to search for or otherwise navigate to http://en.wikipedia.org/wiki/[something that doesn't exist on my keyboard]. – David Richerby Nov 1 '16 at 8:55
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    @guidot the English equivalent is a section under "Diameter". I've added the link – Chris H Nov 1 '16 at 10:05
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It's the symbol for Durchmesserzeichen - it denotes either

  1. The arithmetic mean (average) or
  2. The geometric diameter.

Context is key, in your diagram it's the average value as it's about statistics. Should you find the symbol in a technical drawing, for example, it's probably the diameter of a hole, bolt or similar.

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    The same glyph may be used to denote an empty set in mathematics, or zero (slashed zero). – aventurin Oct 31 '16 at 21:55
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    @aventurin looks the same, but is technically another unicode character. See the link in my answer. – Stephie Oct 31 '16 at 22:10
  • Note that (for obvious reasons) the diameter symbol (and by extension the mean as they share a symbol) should be a slashed circle. In general a slashed zero or would be based on an ellipse, and a slashed O (Danish etc.) may be either an ellipse or a circle. The empty set symbol has yet another unicode position (see linked article). – Chris H Nov 1 '16 at 9:52
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This is not a German character.

In some Scandinavian languages "Ø" is a letter designating a vowel.

What you are reading is a symbol denoting the average.

As others have indicated, the O with a stroke is used in German texts to abbreviate 'Durchschnitt' (average). I do not know whether this symbol coincides with the Scandinavian letter in Unicode.

In fact, the usage seems to be non-uniform: https://en.wikipedia.org/wiki/%C3%98#Similar_letters The Wikipedia article indicates that the average symbol is indeed different from the Scandinavian letter.

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