Hello Dave, no, Philipp was completely right, like him you also found 2.7µV/V for 95% for the 8508A and the 8588A. I simply grabbed the 8558A specification by accident, which is worse, because it is intended for the 3458A market, as a system DMM in manufacturing lines. Anyhow, these 2.75ppm/year is worse than the performance of the LTFLU reference alone, as it includes the drift of the other components. Frank