Most chemists use the residual protonated solvent peak to reference their spectra, but in two dimensional heteronuclear spectra, like HMBCs, the residual solvent peak is often distorted or not present at all. The 1H dimension of such experiments can usually be referenced by aligning it to a 1D 1H spectrum. The heteronuclear dimension, however, is more difficult to reference correctly. The best way to reference such spectra is to use indirect referencing to calculate the chemical shifts based on the frequency ratio of the nuclei involved.
