In this test, nine data points are included: near the energy minimum and near the classical turning points for the four lowest vibrational levels. These points were selected in the intuitive belief that they are good for reproducing the vibrational levels. Polynomials are used to interpolate and to extrapolate the data. With low-order polynomials, using a guiding potential improves accuracy substantially. Except for the lowest-order polynomials, different guiding potentials provide similar accuracy. These trends may be understood by considering eq. ( ). Low-order polynomials, fM(), recover less information from the high-level data than high-order polynomials recover, leading to heavier reliance upon the information in the guiding potential, g().