This implies that two of the three neutrinos have very closely placed masses. Since only two of the three Δ Δ m 2 are independent, and the expression for probability in equation (13) is not sensitive to the sign of Δ Δ m 2 (as sine squared is independent of the sign of its argument), it is not possible to determine the neutrino mass spectrum uniquely from the phenomenon of flavor oscillation. That is, any two out of the three can have closely spaced masses.