The refractive indices of four minerals (P, Q, R, S) are as follows:
P(α = 1.712, β = 1.721, λ = 1.727),
Q(ε = 1.553, ω = 1.544),
R(α = 1.664, β = 1.672, λ = 1.694) and
S(ω = 1.658, ε = 1.486)
The value of maximum briefringence among all the minerals is ____ (give answer in two decimal places).