Polar coordinates
A point in polar coordinates is (r, θ): how far from the centre, and at what angle. Angles are measured counter-clockwise from the line pointing right (0°), so 90° is straight up and 180° points left. To plot (4, 60°), turn to the 60° spoke and count out four rings.
Polar paper makes curves that are awkward on square paper easy to draw: circles centred on the origin, spirals (r = θ), cardioids (r = 1 + cos θ) and roses (r = cos 3θ). Spokes at 15° land on the angles students use most (30°, 45°, 60°, 90°); 5° spokes are for plotting tables of values.