CURVE FORMULAE D = Degree of Curve 1° = 1-Degree of Curve 2° = 2-Degree of Curve P.C. = Point of Curve P.T. = Point of Tangent P.I. = Point of Intersection I = Intersection of Angle, Angle between Two Tangents L = Length of Curve, from P.C. to P.T. T = Tangent Distance E = External Distance R = Radius L.C. = Length of Chord M = Length of Middle Ordinate c = Length of Sub-Chord d = Angle of Sub-Chord R = L.C./2 sin 1/2 I T = R tan 1/2 I = L.C./2 cos 1/2 I L.C./2 = R sin I/2, D 1° = R = 5730, D 2° = 5730/2, D = 5730/R M = R (1 - cos 1/2 I), = R - R cos I/2 E + R / R = sec I/2, R - M / R = cos I/2 c = 2 R sin 1/2 d, d = c/2R L.C. = 2 R sin 1/2 I, E = R (sec 1/2 I - 1), = R sec I/2 - R Minutes in Decimals of a Degree Inches in Decimals of a Foot