# What is this symbol? **URL:** \ **Category:** Factual Questions\ **Created:** [August 18, 2003, 6:10pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008 "2003-08-18T18:10:59Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![ProjectOmega](https://avatars.discourse-cdn.com/v4/letter/p/b487fb/32.png) [@ProjectOmega](https://boards.straightdope.com/u/ProjectOmega)\ **Post date:** [August 18, 2003, 6:10pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/1 "2003-08-18T18:10:59Z")
Ø \<-- What is this called? How and where is it used? (In case the symbol doesn’t show up on all screens, it’s a circle with a diagonal line through it). ---
**Author:** ![Phlosphr](https://avatars.discourse-cdn.com/v4/letter/p/c68b51/32.png) [@Phlosphr](https://boards.straightdope.com/u/Phlosphr)\ **Post date:** [August 18, 2003, 6:13pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/2 "2003-08-18T18:13:22Z")
It denotes a zero. So you do not get it confused with an “O” usually when hand writing something. I do not know it’s proper name aside from ZERO. ---
**Author:** ![Xgemina](https://avatars.discourse-cdn.com/v4/letter/x/b5e925/32.png) [@Xgemina](https://boards.straightdope.com/u/Xgemina)\ **Post date:** [August 18, 2003, 6:16pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/3 "2003-08-18T18:16:23Z")
I know it is used as a zero, but isn’t it more properly known as “Null” as in a Null Set {Ø} ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [August 18, 2003, 6:17pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/4 "2003-08-18T18:17:28Z")
A cipher, used for zero when the numeral 0 might be confused with the letter O, and used to indicate a null set in mathematics. ---
**Author:** ![ProjectOmega](https://avatars.discourse-cdn.com/v4/letter/p/b487fb/32.png) [@ProjectOmega](https://boards.straightdope.com/u/ProjectOmega)\ **Post date:** [August 18, 2003, 6:24pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/5 "2003-08-18T18:24:59Z")
Are there other uses? For instance, I’m pretty sure it’s a regular letter in some languages, like in Danish. Specifically, I’m looking for deeper “symbolic” meanings. Like you have the Greek symbol omega. It’s a letter, it’s a mathematical symbol (used in electronics?), but it also has a sort of literary association with “the end”. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 18, 2003, 6:25pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/6 "2003-08-18T18:25:11Z")
It’s also a Danish and Norwegian [vowel](http://www.wikipedia.org/wiki/%D8). ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 18, 2003, 6:27pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/7 "2003-08-18T18:27:33Z")
Oh you want symbolic meanings. Ok, well in electrical engineering, it is the symbol for “phase”, as in a 3Ø motor. ---
**Author:** ![cybersnark](https://avatars.discourse-cdn.com/v4/letter/c/b9e5f3/32.png) [@cybersnark](https://boards.straightdope.com/u/cybersnark)\ **Post date:** [August 18, 2003, 7:43pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/8 "2003-08-18T19:43:35Z")
Isn’t it also the lower case Greek letter Phi? ---
**Author:** ![Shade](https://avatars.discourse-cdn.com/v4/letter/s/2bfe46/32.png) [@Shade](https://boards.straightdope.com/u/Shade)\ **Post date:** [August 18, 2003, 7:54pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/9 "2003-08-18T19:54:07Z")
As a mathematician I consider that symbol the Greek letter Phi (as cybersnark says), _which is used to denote an empty set_. However I am unable to find confirmation in mathworld. It’s possible it’s two different symbols that look the same. I also thought that in a zero the crossbar didn’t protrude beyond the circle. But I’m really not sure of this. ---
**Author:** ![John\_Kentzel-Griffin](https://avatars.discourse-cdn.com/v4/letter/j/ccd318/32.png) [@John\_Kentzel-Griffin](https://boards.straightdope.com/u/John_Kentzel-Griffin)\ **Post date:** [August 18, 2003, 7:56pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/10 "2003-08-18T19:56:59Z")
> [@](#): > > \*Originally posted by \*\*\*Xgemina \*\* > I know it is used as a zero, but isn’t it more properly known as “Null” > > as in a Null Set {Ø} \*\* Ø and { } both represent the null set, the set with no elements. {Ø} is a set with one element, that element being the null set. ---
**Author:** ![Monty](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/monty/32/47_2.png) [@Monty](https://boards.straightdope.com/u/Monty)\ **Post date:** [August 18, 2003, 7:59pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/11 "2003-08-18T19:59:16Z")
Well, as [Group 47, Symbol 4](http://www.symbols.com/encyclopedia/47/474.html), it has a number of meanings, listed at that link. It’s also one of the symbols for the International Phonetic Alphabet. ---
**Author:** ![Mort\_Furd](https://avatars.discourse-cdn.com/v4/letter/m/8e8cbc/32.png) [@Mort\_Furd](https://boards.straightdope.com/u/Mort_Furd)\ **Post date:** [August 18, 2003, 7:59pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/12 "2003-08-18T19:59:19Z")
That symbol is also used on some encrypted two-way radio and telephony equipment to denote operation in encrypted mode. ---
**Author:** ![Brad\_Amundsen](https://avatars.discourse-cdn.com/v4/letter/b/dbc845/32.png) [@Brad\_Amundsen](https://boards.straightdope.com/u/Brad_Amundsen)\ **Post date:** [August 18, 2003, 8:08pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/13 "2003-08-18T20:08:01Z")
“Not” ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [August 18, 2003, 9:39pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/14 "2003-08-18T21:39:43Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > Oh you want symbolic meanings. Ok, well in electrical engineering, it is the symbol for “phase”, as in a 3Ø motor. \*\* Nope. The symbol for phase is the Greek letter phi which is different from the nordic O used for the null set. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [August 18, 2003, 11:04pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/15 "2003-08-18T23:04:42Z")
> [@](#): > > \*Originally posted by cybersnark \* > \*\*Isn’t it also the lower case Greek letter Phi? \*\* No. > [@](#): > > \*Originally posted by sailor \* > \*\*The symbol for phase is the Greek letter phi which is different from the nordic O used for the null set. \*\* Correct. Phi has a **vertical** line. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [August 18, 2003, 11:09pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/16 "2003-08-18T23:09:43Z")
Null (and assorted meanings) = **Ø** (and when appearing as lower case in Scandinavian languages, **ø** ) Phi = **[symbol]F f[/symbol]** (upper and lower case) ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 18, 2003, 11:31pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/17 "2003-08-18T23:31:17Z")
> [@](#): > > \*Originally posted by sailor \* > \*\*Nope. The symbol for phase is the Greek letter phi which is different from the nordic O used for the null set. \*\* I think you’ll find the symbol Ø used far more frequently in the industry than _phi_. I worked for a company that made, among other things, three-phase transformers. There were invariably marked ØA, ØB and ØC on the terminals. This symbol was also used on customer-supplied drawings for three-phase units from places like Allied Signal, G.E.C. Marconi and Kearfott Guidance & Navigation, so it wasn’t a mere idiosyncracy of my company. I have the definitive work ona this topic, _The Electrical Engineer’s Reference Book_, but it’s packed away and I can’t look it up right now, but I’m pretty sure they use the symbol Ø for phase as well. ---
**Author:** ![Xgemina](https://avatars.discourse-cdn.com/v4/letter/x/b5e925/32.png) [@Xgemina](https://boards.straightdope.com/u/Xgemina)\ **Post date:** [August 18, 2003, 11:40pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/18 "2003-08-18T23:40:20Z")
> [@](#): > > \*Originally posted by DrMatrix \* > \*\*Ø and { } both represent the null set, the set with no elements. {Ø} is a set with one element, that element being the null set. \*\* Arghh, thats right, thanks **DrMatrix**. I can hear my 8th grade algebra teacher right now: intoning (over and over), “One or the other but not both.” Mrs. Gill would undoubtably be very disapointed in me right now. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [August 18, 2003, 11:41pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/19 "2003-08-18T23:41:22Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > I think you’ll find the symbol Ø used far more frequently in the industry than _phi_. People may be using the wrong symbol but they call it phi. i have never heard phase called anything else. If they are using another symbol it means they are using the wrong symbol for phi. Or what did you call phase? Null? I don’t think so. It is the Greek letter phi. Except maybe some people don’t know how to write it correctly or maybe they are using the wrong symbol. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [August 18, 2003, 11:56pm UTC](https://boards.straightdope.com/t/what-is-this-symbol/196008/20 "2003-08-18T23:56:10Z")
Well, I did an unscientific survey with Google: 3Ø power - 4920 hits. 3F power - 1890 hits. It may be, as you say, the wrong symbol, but it’s a popular wrong symbol–more so even than the “correct” one. I’d even go so far as to say at this point Ø _is_ the correct symbol by default, purism be damned. [Next page](https://boards.straightdope.com/t/what-is-this-symbol/196008.md?page=2)