PI()
 Returns pi with the highest degree of accuracy
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 Syntax

     PI() --> nPI

 Returns

     PI() returns the pi value with the highest degree of accuracy.

 Description

     This function simplifies calculations when the most accurate pi value is
     required.

 Example

     Show the accurate display for the pi value:

     ? STR(PI(), 18, 15)      // Result:  3.141592653589793