In the article "The World's Longest Continued Series of Sea Level Observations" (M. Ekman, Paleogeography, 1988:73–77), the mean annual level of land uplift in Stockholm, Sweden, was estimated to be 4.93 +_ 0.23 mm for the years 1774–1884 and to be 3.92 +_ 0.19 mm for the years 1885–1984.
1. Estimate the difference in the mean annual uplift between these two time periods, and find the uncertainty in the estimate.