On a definition of the SI second based on several transitions

Abstract The redefinition of the SI second is expected in the near future due to progress in time and frequency metrology. One promising option is to use several transitions to define the SI second. However, the proposed definitions use a 'constant' that is unnecessary for such a definition, is not a constant in value between possible redefinitions and has no physical meaning, which may be controversial properties. Therefore, this paper proposes alternative wording for the definition of the SI second that does not directly use such a constant, in order to improve a possible definition based on several transitions.