The existence or absence of continuum flux in an IUE echellogram is determined by the order registration module. Because interorder-overlap flux can affect background determinations only for continuum images, in the noncontinuum case BASISMOD does not go through a Pass 1 step. The background estimates for these images are determined by sampling the interorder background on the long-wavelength side (spatial) of a given order with a one-pixel slit. A 7th degree Chebyshev solution is then computed for this nearly continuous array of interorder pixels. Note that tests show that some minor contamination from strongly saturated emission lines has been detected in neighboring orders.