This is documentation for Mathematica 8, which was
based on an earlier version of the Wolfram Language.
View current documentation (Version 11.2)


gives the size of an ulp for numbers near x.
  • The difference between two consecutive machine numbers is called an ulp, which stands for unit in the last place.
  • The size of an ulp varies depending on where you are in the set of machine numbers. Between 1 and 2 an ulp is equal to $MachineEpsilon, between 2 and 4 an ulp is equal to $MachineEpsilon, etc.