Length of Parallels
The default tab, these sliders control the length of parallels. Dragging to the left shortens the length of parallels and dragging to the right lengthens them. Lengths are relative: 0 represents a parallel that has no length (for example, the poles on some projections) and 1 represents the maximum possible length.
Use the Poles and Equator dialog in the Options button to adjust the curvature of meridians at poles and at the equator.