These two rulers to help with drawing lines, cirles, and ellipses.
Only one can be used at a time. They can be accessed through hotkeys, R for the straight ruler and E for the elliptical. Before painting, the rulers displays guidelines; however, once you start painting, they disappear. Once you finish painting, they reappear. The last location of a ruler is saved, so that the next time you access a ruler it appears at the same place.
When a ruler is activated, at the top of the canvas, a hub appears. It provides the X and Y positional coordinates, along with the angle of rotation. The elliptical ruler contains additional A and B coordinates for the distance of each side from the center of the ellipse. As changes are made to the rulers, these values update.