So how do you prevent all these headaches? First, understand that barrel misalignment is measured with respect to the rotation axis of the extruder drive quill. In other words, a perfectly straight, brand-new barrel can still easily be misaligned to the rotation axis of the quill, with potentially ruinous results. One common, lingering misconception is that alignment can be indicated by use of a level. Not so; this measures only the levelness of the outside of the barrel, which has virtually nothing to do with the alignment of the barrel centerline relative to the rotation axis of the extruder drive quill.