They seem to have come with some nice algorithm to connect the graph dots. The problem: When you draw the graph using a naive formula putPixel(x, y(x)) you get isolated dots. Therefore you have to draw tiny lines between the points to get a nice smooth curve instead of isolated dots. But then there is the question of which points to connect – for example in tan(x) you can’t connect the last point on the ‘upper right hand’ with the first one coming from the bottom. This is surprisingly hard to solve simply (at least it was for me). Most packages simply resign – try zooming out a tan(x) to see the erroneous vertical connecting lines. Google does it right even in high zoom ratios. How do they do it?