and settings are typically the primary sources of bad welds, which can be countered by improving a welding operator's techniques, set-ups, and knowledge base. Bad welds contain porosity, pinholes, undercut edges, excessive penetration, spatter, slag on the weld surface, lack of fusion, heat marks, overlap, and more.
These defects and inconsistencies can be controlled by following the examples of professional welding operators with greater field experience than you do. The accumulated knowledge of veteran welders significantly outweighs studying other resources or technical books. Understanding welding theory is essential, but the guidance of a professional is the best way to ensure most of your current work consists of good welds, and bad welds have become a thing of the past!