((Δ ((%)^13)C=(Subscript[(((%)^13)C), t])-(Subscript[(((%)^13)C), 0])={[(Subscript[((δ^13)C), t])-(Subscript[((δ^13)C), 0])]/1000}×(Subscript[R, PDB])×100=((Δ^13)C×(Subscript[R, PDB]))/10)\[Placeholder](Formula   8))