The prime symbol ( ′ ), double prime symbol ( ″ ), triple prime symbol (  ), quadruple prime symbol (  ) etc., are used to designate several different units and for various other purposes in mathematics, the sciences, linguistics and music. The prime symbol should not be confused with the apostrophe, single quotation mark, acute accent, or grave accent; the double prime symbol should not be confused with the double quotation mark, the ditto mark, or the letter double apostrophe. 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 not, so they should not be interchanged.