The Nab collaboration proposes to measure the electron-neutrino correlation parameter a with a precision of δa/a = 10^−3 and the Fierz interference term b to δb = 3 × 10^−3 in unpolarized free neutron β decay. These results are expected to lead to a new, precise, independent determination of the ratio λ = GA/GV that will sensitively test CKM unitarity. A long asymmetric spectrometer guides the decay products to two large area silicon detectors in order to precisely determine the electron energy and proton momentum. The Nab apparatus is under installation on the Fundamental Neutron Physics Beamline at the SNS at ORNL and commissioning will begin in the near future. An overview of the Nab experiment, systematics effects associated with spectrometer magnetic fields, and the first tests of the spectrometer will be presented.