Systematic evaluation of a strontium optical lattice clock at 1x10$^{-16}$

We have recently completed an evaluation of the uncertainty of a $^{87}$Sr optical lattice clock at the 1x$10^{-16}$ fractional level, surpassing the best current evaluations of Cs primary standards. The evaluation was performed using a remote comparison of optical clocks over km-scale urban distances. This allowed us to evaluate the Sr clock located at JILA, against the Ca optical clock operated $\sim$4km away at NIST via an optical fiber link. We will report on the observation of density-dependent effects in the doubly spin-polarized (fermionic) sample. Using a single spin state, and by varying the excitation fraction, we have found experimental parameters for which the density shift of the clock transition is consistent with zero.