Life aboard an 18th-century British sailing ship left much to be desired. Salt caked your clothes. Rats shared your food. Hard, sun-baked days retreated into cold, damp nights. You could fall off a foremast, blow over a bow, drown in the deep, succumb to scurvy, or be vanquished by venereal disease. All the while, you counted. You counted the dawns at sea and the stars at dusk. You counted knots, fathoms, and degrees. Ocean crossings became makeshift research studies, where sailors quantified the lengthy distances between ports and the even longer durations between paychecks.