# NAG CPP Interfacenagcpp::machine::precision (x02aj)

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## 1Purpose

precision returns $\epsilon$, the value machine precision.

## 2Specification

#include "x02/nagcpp_x02aj.hpp"
double precision()

## 3Description

precision returns machine precision, computed as $\epsilon =\frac{1}{2}×{b}^{1-p}$, where $b$ is the arithmetic base (see x02bhf (no CPP interface)) and $p$ is the number of significant base-$b$ digits (see x02bjf (no CPP interface)).
It is important to note that the definition of $\epsilon$ here differs from that in ISO Fortran 95 (1997).

## 4References

ISO Fortran 95 (1997) ISO Fortran 95 programming language (ISO/IEC 1539–1:1997)

None.

None.

Not applicable.

## 8Parallelism and Performance

Please see the description for the underlying computational routine in this section of the FL Interface documentation.