· The microstructure and compositions of the phases present are shown on the partial diagram for a Cu-35 wt% Ni alloy ( 65 wt% Cu, 35 wt% Ni)
· The equilibrium mass fraction of each phase present in a two phase zone is estimated using the "Lever Rule."
· For a zone with two phases A, B present, total mass conservation requires:
W_A + W_B = 1
where W_I is the mass fraction of I.
· From conservation of constituents: 
W_A C_A + W_B C_B = C₀ 1