Nowadays many children meet the idea of a locus at an early age. This is because of the great (and deserved) success of LOGO as an educational tool to introduce geometrical ideas to young children. The challenge is to devise lists of instructions to make a ‘turtle’ move in a certain way. Originally the turtle would have been an actual mechanical object moving on the floor. It is now more usually an image on a computer screen. The mechanical turtle held a pen which marked out its path; the computer version* whether it looks like a cartoon turtle or an arrowhead (or even remains ‘hidden’) leaves as its trail a series of dots showing where it has been. The end product drawn on the floor or the screen is thus seen as the path of a point moving according to a prescribed set of rules. In this way children are encouraged to think of any geometrical diagram—whether it is a square or a hexagon, a rectangle or a house, a star or a circle—as a locus. Geometry is built up from collections of points.