Tonne per centimeter immersion (TPC)

TPC is the mass that must be loaded or discharged to change mean draft by one centimeter: $TPC = (A_W \cdot \rho) / 100$, with waterplane area $A_W$ in m^2 and density $\rho$ in t/m^3. It comes straight from the curves of form and lets a mate convert a planned parcel weight into a draft change, or read off the deadweight available before the marks immerse. TPC grows with draft as the waterplane widens.