This is documentation for Mathematica 8, which was
based on an earlier version of the Wolfram Language.
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Precision & Accuracy Control
Mathematica has sophisticated built-in automatic numerical precision and accuracy control. But for special-purpose optimization of numerical computations, or for studying numerical analysis, Mathematica also allows detailed control over precision and accuracy.
N numerical evaluation to specified precision and accuracy

PrecisionGoal, AccuracyGoal precision and accuracy goals for computations
WorkingPrecision precision to use inside algorithms

Precision find the precision of a number
Accuracy find the accuracy of a number

Chop set sufficiently small numbers or imaginary parts to zero
SetPrecision, SetAccuracy reset precision or accuracy of a number
\$MinPrecision, \$MaxPrecision settable global precision bounds
\$MaxExtraPrecision maximum extra precision to use inside exact algorithms

Machine Numbers
MachinePrecision symbol representing machine precision
MachineNumberQ test if a number is a machine number
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