The NMR scale (d, ppm)
       w - wref
d =    ppm (parts per million)
          wref
Instead use a relative scale, and refer all signals (w) in the spectrum to the signal of a particular compound (wref).
Bo  >>  Bloc    --   MHz   compared to Hz
Comparing small changes in the context of a large number is cumbersome
Tetramethyl silane (TMS) is a common reference chemical
H
3
C
S
i
C
H
3
C
H
3
C
H
3
IMPORTANT: absolute frequency is field dependent (n = g Bo / 2p)