The core was loaded with fuel and reflector elements with subcriticality ensured by temporary neutron absorbers. Pulsed-neutron measurements initially showed the core to be more subcritical than calculated. Adjustment of the calculational model by including the correct reflector impurities led to good agreement between calculated and measured values of the multiplication constant and prompt neutron generation time. Axial fluxes showed consistent good agreement between calculated and measured values for a variety of configurations, but the ratios of average regional fluxes in the top half of the core to their respective regional averages in the bottom half differed from the calculated ratios by as much as 10%. The helium pressure coefficient was essentially zero. The calculated and measured isothermal temperature coefficients up to 300°F agreed within 3%. Control rod calibrations using the reactivity computer were satisfactory only for the central rod pair. Peripheral rod pairs were calibrated by comparison to the central rod pair.