I've never been trained on determining ones position using just a sextant and a clock, but I'm given to understand that it builds character.
in 1980, when gps technology was financially beyond the reach of the average sailor, i sailed across the atlantic. from gibraltar to the madeira islands to the british virgin islands. we used a plastic sextant, a shortwave radio tuned to the bbc who, at that time, counted down the seconds to every g.m.t. hour, the aforementioned books of declination, and did the math by hand. we hit the anegada passage right on the money after a crossing of 40 days.
yes, it builds character. one hand for the boat and one hand for you is challenging when it takes two hands to use the sextant, never mind the radio.