Assert.AreEqual <double, double, int>
As a developer I want to test for equality of doubles, using a relative precision indicator (as opposed to an absolute delta).
Assert(double, double, int)
Assert.AreEqual(1.0, 1.000000001, 8) // will not fail
Assert.AreEqual(100000.0, 100000.0001, 8) // will not fail
In both cases the first 8 significant digits are the same.
Another method signature that go with this is of course:
Assert(double, double, int, string, params object)