Prime (symbol) facts for kids
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Prime




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The prime symbol ( ′ ), double prime symbol ( ″ ), triple prime symbol ( ‴ ), quadruple prime symbol ( ⁗ ) etc., are used to designate units and for other purposes in mathematics, the sciences, linguistics and music.
Although similar in appearance, the prime symbol should not be confused with the apostrophe ( ’ or ' ), single quotation mark ( ' or ‘ or ’ ), acute accent ( ´ ), or grave accent ( ` ); the double prime symbol should not be confused with the double quotation mark ( “…” or "…" ), the ditto mark ( ” ), or the letter double apostrophe ( ˮ ). The prime symbol is very similar to the Hebrew geresh, but in modern fonts the geresh is designed to be aligned with the Hebrew letters and the prime symbol is not, so they should not be interchanged. All of these similarappearing symbols have different meanings, and their charactercodes are treated differently by typesetting and font rendering software.
Designation of units
The prime symbol ( ′ ) is commonly used to represent feet (ft) and arcminutes (arcmin). However, for convenience, a ( ' ) (single quote mark) is commonly used.
The double prime ( ″ ) represents inches (in) and arcseconds (arcsec). However, for convenience, a ( " ) (double quotation mark) is commonly used.
Thus, 3′ 5″ could mean 3 feet and 5 inches (of length), or 3 minutes and 5 seconds (of arc). As an angular measurement, 3° 5′ 30″ means 3 degrees, 5 arcminutes and 30 arcseconds.
The triple prime ( ‴ ) in watchmaking represents a ligne or 1/12 of an inch. It is also occasionally found in historical astronomical works to denote thirds (^{1}⁄_{60} of a second of arc).
Likewise, a quadruple prime ( ⁗ ) denotes fourths (^{1}⁄_{60} of a third, a convention already used by Jamshīd alKāshī).
 See also: Positional notation#Sexagesimal system