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Why is the plural used in this article's title? (I've created a redirect page with the singular counterpart. Maybe the "move" button should be used to interchange the two roles?) Michael Hardy 20:45, 2 January 2007 (UTC)[reply]

Setting circles come in pairs and as far as I know they have always referred to in plural - and there are exceptions to Wikipedia:Naming conventions (plurals) re: "Binoculars, Scissors, Trousers, Fireworks".

• A google search brings up 25,700 instances for "setting circle" [1] (and they seem to be references to one of them re:"I am looking for a 6" R. A. setting circle")

• A google search brings up 106,000 instances for "setting circles" [2] with usage such as "Build Your Own Digital Setting Circles... It's worth noting that digital setting circles do not move your telescope..."

• according to Answers.com the "McGraw-Hill Dictionary of Scientific and Technical Terms" has them listed as:

setting circle (′sed·iŋ ′sər·kəl)

(engineering) A coordinate scale on an optical pointing instrument, such as a telescope or surveyor's transit.

So it looks kind of 50-50 to my totaly non english major mind ;^). Could go either way. A little further research for evidence or Wikipedia WP:STYLE may help here. Halfblue 19:21, 17 January 2007 (UTC)[reply]

I've always known them as 'setting circles'. As Halfblue says they come in pairs. There is the Right Ascension (RA) setting circle (sky equivalent of terrestrial longitude) and the Declination setting circle (sky equivalent of terrestrial latitude). Also the RA circle has 2 scales (at least in transportable telescopes) one for the Northern hemisphere and another going round the other way for use in the Southern hemisphere. Also not all setting circles are Equatorial (RA/Dec) - If Dobsonian telescope users have circles fitted they are Altitude/Azmuth and then they use a computer to convert from RA/Dec to Alt/Az. Finally if I do a Google search on "how to use setting circle" (quotes included) I get one find (which might be a typing error). If I search on "how to use setting circles" I get 18 hits. GraL (talk) 15:53, 8 September 2008 (UTC)[reply]

The position of an object on the night sky is uniquely determined by two orthogonal coordinates, requiring the alignment of two axes to match the telescope orientation. Hence the plural form. Praemonitus (talk) 04:39, 18 September 2021 (UTC)[reply]