NMR instruments typically have a constant Rf and a variable Bo. A proton should absorb Rf of 60 MHz in a field of 14,093 Gauss (1.4093 T) Each unique probe nucleus (H perhaps)will come into resonance at a slightly different and a very small percentage of-the Rf. All protons come into resonance between 0 and 12/1,000,000(0-12 ppm)of the RNMR instruments typically have a constant Rf and a variable B0 . A proton should absorb Rf of 60 MHz in a field of 14,093 Gauss (1.4093 T). Each unique probe nucleus (1H perhaps) will come into resonance at a slightly different - and a very small percentage of - the Rf. All protons come into resonance between 0 and 12/1,000,000 (0 – 12 ppm) of the Rf