CUSUM Analysis of Operative Time. The blue curve represents the cumulative deviation of each case’s operative time from the overall mean. The trajectory reveals three distinct phases: an initial learning phase with a steady rise in CUSUM values; a stabilization phase with a plateau around case 265; and a subsequent optimization phase characterized by a marked decline in CUSUM values. The red dotted line indicates the inflection point at case 265, marking the transition beyond the learning phase.