Directions: Enter values for span (ft), spacing, species, grade, live and dead load (psf), duration of load and wet service conditions, allowable deflection criteria (e.g., span/360 for live load only), and select dimensions and properties from either the 2005 or 2012 National Design Specification (NDS).irections: Enter values for span (ft), spacing, species, grade, live and dead load (psf), duration of load and wet service conditions, allowable deflection criteria (e.g., span/360 for live load only), and select dimensions and properties from either the 2005 or 2012 National Design Specification (NDS).