Before revision: Over the transatlantic leg of his voyage - a distance of about - he was able to navigate with a cumulative error of about in landfall, or less than one percent of the distance travelled, by computing his position at hourly intervals by dead reckoning with the induction compass .
After revision: Over the transatlantic leg of his voyage - a distance of about - he was able to navigate with a cumulative error of about in landfall, or about one half of one percent of the distance travelled, by computing his heading at hourly intervals for a dead reckoning estimate of position .