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Ulp

Ulp[x]
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 $MachineEpsilon, between 2 and 4 an ulp is equal to 2$MachineEpsilon, etc.