The accuracy and reliability of difference NMR spectroscopy can be substantially improved by a simple correction based on changes in the lineshape of an internal reference line. This reference lineshape adjusted (RLSA) method is experimentally demonstrated to behave according to theoretical predictions under variations in drift of the main magnetic field, in rf power, in homogeneity of the main field, in spinning side bands, in detector phase, and in sweep rate. The RLSA method is experimentally demonstrated to automatically compensate for changes in all these instrumental parameters provided H, is sufficiently small that saturation is avoided. In addition, the internal reference must be constant in composition, concentration, and resonance position, and must be totally resolved from the rest of the spectrum. Under these conditions, the RLSA method is shown to give difference spectra that are visibly superior to simple difference spectra.