pub fn t_chart(inter_event_times: &[f64]) -> Option<TChart>Expand description
Compute the T chart from inter-event times.
§Formulas (exponential distribution percentiles)
- t̄ = mean(tᵢ)
- UCL = t̄ · (−ln(0.00135)) ≈ t̄ · 6.6077
- LCL = max(0, t̄ · (−ln(0.99865))) ≈ t̄ · 0.00135
The constants are derived from the 0.00135 and 0.99865 quantiles of the standard exponential distribution, matching the ±3σ tail probability used in Shewhart charts (α/2 = 0.00135).
§Returns
None if fewer than 3 observations or any time is non-positive.
§Reference
Borror, C.M., Keats, J.B. & Montgomery, D.C. (2003). “Robustness of the time between events CUSUM”, International Journal of Production Research 41(15), pp. 3435-3444.