Tabular CUSUM Architecture & Decision Limits
Tabular CUSUM maintains two running sums: C⁺ for positive upward drift and C⁻ for downward drift. The reference allowance is typically K = 0.5σ, and the decision threshold is H = 4.77σ.
Advanced Category: Statistical Process Control (SPC) • ~8 min read
Cumulative Sum (CUSUM) Chart
Rapidly detect persistent subtle process drift before standard Shewhart charts signal.
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Q:
Why is CUSUM superior to Shewhart charts for detecting small process shifts?
Standard Shewhart charts only evaluate the current point and require large shifts (1.5σ to 3σ) to trigger quickly. The Cumulative Sum (CUSUM) chart accumulates deviations from target over time, detecting subtle drifts (0.5σ to 1.5σ) up to 4 times faster.
Reference Value (K)0.2500.5 × σ
Decision Interval (H)2.3854.77 × σ Threshold
Max C+ Accumulation10.10Upper Sum
Shift Signal Status5 Shift AlertsSmall-Shift Detection
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