  We consider the effect of regularization by interval truncation on the
spectrum of a singular non-selfadjoint Sturm-Liouville operator. We present
results on spectral inclusion and spectral exactness for the cases where the
singularity is in Sims Case II or Sims Case III. For Sims Case I we present a
test for spectral inexactness, which can be used to detect when the interval
truncation process is generating spurious eigenvalues. Numerical results
illustrate the effectiveness of this test.
