  A Mach-Zender interferometer with a gaussian number-difference squeezed input
state can exhibit sub-shot-noise phase resolution over a large phase-interval.
We obtain the optimal level of squeezing for a given phase-interval
$\Delta\theta_0$ and particle number $N$, with the resulting phase-estimation
uncertainty smoothly approaching $3.5/N$ as $\Delta\theta_0$ approaches 10/N,
achieved with highly squeezed states near the Fock regime. We then analyze an
adaptive measurement scheme which allows any phase on $(-\pi/2,\pi/2)$ to be
measured with a precision of $3.5/N$ requiring only a few measurements, even
for very large $N$. We obtain an asymptotic scaling law of $\Delta\theta\approx
(2.1+3.2\ln(\ln(N_{tot}\tan\Delta\theta_0)))/N_{tot}$, resulting in a final
precision of $\approx 10/N_{tot}$. This scheme can be readily implemented in a
double-well Bose-Einstein condensate system, as the optimal input states can be
obtained by adiabatic manipulation of the double-well ground state.
