Vessel Volume & Level Calculation -
Estimates Volume filled in a Horizontal/ Vertical Vessel with
Ellipsoidal (2:1 Elliptical), Spherical (Hemispherical),
Torispherical (ASME F&D, Standard F&D, 80:10 F&D) and Flat
heads. For horizontal orientation, volume can be calculated for
both convex, a > 0 and concave, a < 0 heads.