This version of circuit_offset/2 uses the native Gecode indexing, which starts from 0. This is different from normal ECLiPSe's indexing, which starts from 1. Offset is not adjusted in this version. This version of the constraint is provided for completeness, in case the user is using native Gecode indexing in their code, so that Offset does not need to be adjusted manually by the user.
See circuit_offset/2 for a more detailed description of this predicate.