Slocum had no time piece other than an trashed alarm clock that only had the hour hand. He navigated using moon shots that were extraordinarily hard to compute but didn't require a chronometer. The tables for computing fixes from the moon were dropped from Bowditch not too long after Slocum made his voyage. The calculations were so difficult and reliable, cheap chronometers so prevalent by the late 1800s that no one wanted to use the technique anymore. Slocum's book downplays the skill and tenacity it took to take a rotten oyster boat so long abandoned it had a tree growing out of it and turn it into an oceangoing sailboat and sail it around the world.