“…The Zones graph consists of eight zones (four on each side of the center line) (Zhang et al, 2018), bounded by a central line, the limits: 1-sigma, 2-sigma and 3-sigma. Its use is recommended for practical use because of its performance, simplicity, efficiency, ease of use and understanding (Ho & Case, 1994). For the interpretation of the Zones graphs, the scoring rules (Davis et al, 1990), described in Table 2, were used, and a graph is considered out of statistical control when it reaches 8 points.…”