In the PRIMUS project, we are taking spectra of thousands of galaxies simultaneously. Because we know the properties of the instrument and of our slitmask, we know pretty well where those spectra are on the CCD images we read out of the IMACS instrument. However, we do not know exactly; there can be offsets, scale differences, rotations, and shear. I spent the day writing automated, robust code to find the spectra in the CCD images, given a slitmask file and a set of IMACS CCD readout images. The low dispersion of our spectra makes everything more difficult—except this, which is in fact made easier by low (and non-linear) dispersion.