The use of the deuterium (lock) channel, so the H signal of the deuterated solvent, and the Ξ value of the absolute scale is a form of internal referencing and is particularly useful in heteronuclear NMR spectroscopy as local reference compounds may not be always be available or easily used (i.e. liquid NH 3 for N NMR spectroscopy). This system, however, relies on accurately determined H NMR chemical shifts enlisted in the spectrometer software and correctly determined Ξ values by IUPAC. A recent study for F NMR spectroscopy revealed that the use of the absolute scale and lock-based internal referencing led to errors in chemical shifts. These may be negated by inclusion of calibrated reference compounds.