Arch heights (rises) and semiaxis b remain constant.
Values of y and values of parameter t at corresponding
Framing Points are equal.
Values of semiaxis a and distances to Framing Points
along the xaxis shear according to the formula:
Valley Run = Common Run ÷ sin Plan Angle
Slopes of asymptotes and slopes at corresponding
Framing Points are governed by the formula:
Valley Pitch = Common Pitch × sin Plan Angle

