ulp

This is the unit of the least significant digit in this value’s significand. For most numbers x, this is the difference between x and the next greater (in magnitude) representable number. There are some edge cases to be aware of:

• If x is not a finite number, then x.ulp is NaN.

• If x is very small in magnitude, then x.ulp may be a subnormal number. If a type does not support subnormals, x.ulp may be rounded to zero.

• greatestFiniteMagnitude.ulp is a finite number, even though the next greater representable value is infinity.

This quantity, or a related quantity, is sometimes called epsilon or machine epsilon. Avoid that name because it has different meanings in different languages, which can lead to confusion, and because it suggests that it is a good tolerance to use for comparisons, which it almost never is.