Why do a precision measurement of delta m(atm)**2 in the electron-neutrino and anti-electron-neutrino disappearance channel?

We discuss why high precision measurements of {delta}m{sub atm}{sup 2} in the {nu}{sub e}/{bar {nu}}{sub e} disappearance channels would be desirable in conjunction with the {delta}m{sub atms}{sup 2} high precision measurements that will be performed in the {nu}{sub {mu}} and {bar {nu}}{sub {mu}} disappearance channels by long baseline experiments such as T2K and NOvA. We show that if these measurements can achieve the challenging precision of about 0.5%, it will be possible to determine the mass hierarchy of the neutrino sector without the need of matter effects