ISO uses a very simple but powerful tool for quality system standards. This tool is the Plan-Do-Check-Act (PDCA) cycle shown in the figure below. It is also known as the Deming cycle after J.W. Deming, who proposed the concept in the 50s. The entire logic, structure, and sequence of standards like ISO 9001 and ISO 13485 are based on this cycle. Every process or activity needs to pass through these four phases.