This paper describes an algorithm which traces the curve f(x,y) = 0, in a region over which there is a method of calculating f, using a series of straight lines of length one and two times the step size assumed for the graph plotter or display unit. It does this by determining the sign of the function in the region of the curve and plotting a path between positive and negative values. By means of a suitable interpolation formula instead of an explicitly given function this algorithm can also be used for contour plotting over a grid of values.