.NET Framework Class Library
Double..::.Epsilon Field

Represents the smallest positive Double value greater than zero. This field is constant.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)
Syntax

Visual Basic (Declaration)
Public Const Epsilon As Double
Visual Basic (Usage)
Dim value As Double

value = Double.Epsilon
C#
public const double Epsilon
Visual C++
public:
literal double Epsilon
JScript
public const var Epsilon : double
Remarks

The value of this constant is 4.94065645841247e-324.

Two apparently equivalent floating-point numbers might not compare equal because of differences in their least significant digits. For example, the C# expression, (double)1/3 == (double)0.33333, does not compare equal because the division operation on the left side has maximum precision while the constant on the right side is precise only to the specified digits. If you create a custom algorithm that determines whether two floating-point numbers can be considered equal, you must use a value that is greater than the Epsilon constant to establish the acceptable absolute margin of difference for the two values to be considered equal. (Typically, that margin of difference is many times greater than Epsilon.)

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
See Also

Reference

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Community Content

Thomas Lee
Cannot be used for "almost equality" testing
This value is not defined as smallest positive number x, such that x + 1.0 is not equal to 1.0, so Double.Epsilon cannot be used for "almost equality". There exists no constant in the framework whose value is smallest positive number x, such that x + 1.0 is not equal to 1.0.

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