RTY tells you how bad the whole line is; the individual step FPYs tell you where. Because RTY is a product, the step with the lowest FPY drags it down the most, and raising that one step gives the biggest gain for the effort. Comparing step yields side by side is the quickest way to decide where to send the engineer.
The improvement is easy to predict. Replace the weak step's current FPY with a target value and recalculate the product. If routing moves from 0.93 to 0.98 while the other steps stay the same, the new RTY follows directly. This lets you compare projects on paper before anyone spends a week on the floor.
One counting rule keeps the arithmetic honest: FPY counts units, not defects. A harness found with three taping faults at one station is one first-pass failure, not three. Defect counts are useful for fixing the problem, but the yield figure asks whether the unit passed, and it did not.
Standard Procedure
- 1Line up all step FPYs for the same week and circle the lowest.
- 2Recalculate RTY with the lowest step set to a realistic target.
- 3Compare the gain against the effort to decide whether to proceed.
- 4Count units, not defects, when a single harness has several faults at one step.
Lesson Summary
- ✓Rank step FPYs and go after the lowest one first.
- ✓A unit with several defects at one station is still one first-pass failure.