critical ratio

**Critical ratio** is the **dispatch priority metric that compares remaining time until due date with remaining processing time** - it highlights lots at highest risk of tardiness. **What Is Critical ratio?** - **Definition**: Ratio calculated as time remaining to due date divided by remaining work content. - **Interpretation**: Values below one indicate likely lateness without priority intervention. - **Decision Role**: Lower critical ratio generally receives higher dispatch priority. - **Scope Use**: Applied in due-date focused scheduling and service-level control. **Why Critical ratio Matters** - **Lateness Prevention**: Prioritizes at-risk lots before due-date miss occurs. - **Objective Alignment**: Directly supports on-time delivery performance targets. - **Transparency**: Provides interpretable urgency score for operators and planners. - **Dynamic Responsiveness**: Priority automatically changes as time and queue conditions evolve. - **Portfolio Control**: Helps balance urgent and normal lots with quantifiable logic. **How It Is Used in Practice** - **Real-Time Calculation**: Recompute ratios continuously as queue and due-date states update. - **Rule Integration**: Combine with setup and queue-time constraints in weighted dispatch engines. - **Escalation Bands**: Define critical-ratio thresholds for automatic hot-lot promotion. Critical ratio is **a practical urgency metric for due-date driven dispatching** - ratio-based prioritization improves tardiness control and strengthens delivery reliability in dynamic fab environments.