  In the next 10 years medium baseline reactor neutrino experiments will
attempt to determine the neutrino mass hierarchy and to precisely measure
{\theta}_12. Both of these determinations will be more reliable if data from
identical detectors at distinct baselines are combined. While interference
effects can be eliminated by choosing detector sites orthogonal to the reactor
arrays, one of the greatest challenges facing a determination of the mass
hierarchy is the detector's unknown energy response. By comparing peaks at
similar energies at two identical detectors at distinct baselines, one
eliminates any correlated dependence upon a monotonic energy response. In
addition, a second detector leads to new hierarchy-dependent observables, such
as the ratio of the locations of the maxima of the Fourier cosine transforms.
Simultaneously, one may determine the hierarchy by comparing the {\chi}^2 best
fits of {\Delta}M^2_32 at the two detectors using the spectra associated to
both hierarchies. A second detector at a distinct baseline also breaks the
degeneracy between {\theta}_12 and the background neutrino flux from, for
example, distant reactors and increases the effective target mass, which is
limited by current designs to about 20 kton/detector.
