When to use: A simple circular curve connects two tangents through a single arc of radius R and deflection angle Ξ. From these two inputs all geometric elements are fixed: the tangent length T (PI to PC/PT), curve length L along the arc, long chord LC, middle ordinate M, external distance E, and the degree of curve D. Used to lay out roadway, rail, and pipeline alignments. All lengths in US customary feet.