Dead reckoning – estimating where you are likely to be, based on your speed and direction of movement from some fixed and known point – is a process used by mariners and navigators since time immemorial. It is used by ants and homing pigeons and humans, and other species too. In biology, it is known as ‘path integration’ and, if you keep track of your speed and direction of movement, it allows you both to work your way towards a goal and back to your point of origin.1 But it is not a perfect process and errors do occur.
