text: Refer to  for the notation used in this example.
  APT is similar to DEPT in that it detects carbon multiplicity. However, it has additional degeneracies: it gives identical positive signals for C and CH, and identical negative signals for CH and CH. One variation on the basic pulse sequence is shown below.
  The key observation is that since we can again ignore the refocussed chemical shift, the only relevant dynamics occur in the interval with no hydrogen decoupling, where we can consider solely the -coupling. By using an interval twice as long as in the DEPT case, we ensure that a density operator of  at the start of the interval just has its sign inverted following the coupling (since this corresponds to  in the general treatment, and ). The Hamiltonians for the couplings to each of the  separate neighbouring hydrogen atoms commute, so the overall effect is to multiply by a factor . This motivates the alternating sign of the signal mentioned above.