 Spin squeezing can improve the stability of quantum sensors by inducing inter-particle correlations that reduce quantum projection noise, but potential gains in clock stability are substantially reduced when the spin squeezing is non-unitary, and analytic formulas have been derived for the clock performance as a function of squeezing, excess spin noise, and interferometer contrast. This article was authored by Boris Braverman, Akio Kawasaki, and Fladen Vueletic.