A dimensionless parameter used to characterize electromagnetic induction response such that μωσL2=constant, where σ is the conductivity contrast, μ the magnetic permeability, ω the angular frequency, and L is a characteristic linear dimension. A full-scale electromagnetic system and a scale-model analog have the same responses if they have the same induction number. For a 1D (layered) model, the induction number is given by the source-receiver separation R divided by the skin depth: B=R/δ=(μωσ)1/2R; an equivalent quantity in the time domain is β=(μσ/2t)1/2R. For an airborne EM system flown at height h over a thin sheet of conductivity-thickness product σd, the induction number is (μωσdh)1/2. Frequently several dimensionless parameters of this type are equally valid. Also called response parameter.