Trane Ductulator The Trane Ductulator is an accurate, easy-to-use calculating device that aids in laying out air-handling systems, sizing ducts and checking duct systems. Complete with both standard and metric calibrations. This hand-held rotating calculator is used for sizing supply and return duct systems using the equal friction design method. It includes scales for friction loss per unit length, air volume, air velocity, round duct diameter, and rectangular duct diameters. One side uses I-P units, the other side uses SI units. Includes a protective sleeve with ASHRAE recommended design air velocities for system components/applications.