Before revision: Even in later eras, the ship could attempt to limit its divergence by tacking or heaving to, but it was often difficult to keep track by mere celestial navigation before the invention of the marine chronometer .
After revision: in the late 18th centuryEven in later eras, the ship could attempt to limit its divergence by tacking or heaving to, but it was often difficult to keep track by mere celestial navigation before the invention of the marine chronometer .