This info allows us to distinguish among carbons bonded to none, one, two, or three H atoms.
C with 0 appear only in normal spectrum, but not in either DEPT
Methine carbons give normal positive peaks in all three spectra
Methylene carbons give normal peaks in teh normal spectrum, no peaks in the DEPT-90 spectrum, and negative peaks int eh DEPT-135 spectrum
Methyl carbons give normal peaks int he normal spectrum, no peaks in the DEPT-90 spectrum, and normal peaks in the DEPT-135 spectrum