Top: ζ as a function of ν/Δν. Black open symbols: numerical results (Eq. (10)). Red dots: ζ approximated by (Eq. (33)) with χ = 2.5 ycos(π/(ΔΠν)) and y = ν/Δν. Bottom: δν/δν_max as a function of ν/Δν. Black dots: numerical values (Eq. (11)). Red dots: approximate expression for δν/δν_max (Eq. (22)) with ℛ = 0.1785 and ζ given by its numerical values. Blue crosses: δν/δν_max given by Eq. (37) with ℛ = 0.1785 and χ given by Eq. (34).