Definition
A set of standardized work instructions. Three levels: L1 is only on paper / L2 changes the process / L3 irreversible change or Error Proofing device; the goal is L3.
In detail
Standard Operating Procedures (SOP) are documents that specify the standard steps and methods for completing a task. They have three levels: L1 is written procedures only, L2 changes the process, and L3 is irreversible mistake-proofing devices, with the goal of reaching L3. They address the problem of 'inconsistent operations causing quality variation and low efficiency.' On the Six Sigma VRK roadmap, the SOP is the output of step 4 and ultimately lands in Standard Work (SW); L3 represents the highest level of mistake-proofing. The output includes SOP documents, training records, and audit checklists.
Example in practice
A food factory found quality differences between shifts due to varying operator habits. The factory developed SOPs for key processes, first documenting steps in writing (L1), then improving fixtures to simplify operations (L2), and finally installing mistake-proofing devices such as sensors to detect missing components (L3). After implementation, operational consistency greatly improved, quality defects decreased, and new employee training became faster.