Recent Improvements in NIST-Fl and Resulting Accuracies of δf/f<7x10-16

Since our last publication describing the accuracy budget for NIST-FI (a laser-cooled Cs fountain primary frequency standard) the authors have made many improvements resulting in nearly a factor of 2 reduction in the uncertainty in the realization of the SI second. Recently the authors reported a combined standard fractional uncertainty of 0.67times10^-15