Final yield is the share of units that are eventually good when they leave a step, after any rework has been done. Most plants report this figure because it matches what ships. The trouble is that it can look excellent while a large amount of labour, test time and material is being burned fixing things. That unrecorded repair effort is called the hidden factory: a second production line inside your plant that produces nothing new.
Final Yield = (First-Time-Good + Reworked-Then-Good) ÷ Units Entering. FPY = First-Time-Good ÷ Units Entering. The gap between the two is exactly the rework rate. If final yield is 99.0 percent and FPY is 95.0 percent, 4 percent of everything passing through was touched twice. On a line making 800 harnesses a shift that is 32 units a shift, 160 a week, each costing repair minutes and a retest slot.
Tracking FPY alongside final yield makes the hidden factory visible. The repair bench stops being invisible overhead and becomes a measured loss with a cost attached, which is the only way to get a budget to remove it.
Standard Procedure
- 1Record first-time passes, rework-then-pass, and scrap as three separate tallies at each station.
- 2Calculate final yield using first-time passes plus reworked passes.
- 3Calculate FPY using first-time passes only.
- 4Report both numbers side by side and label the gap as rework.
- 5Multiply the rework count by average repair minutes to put a cost on the hidden factory.
Lesson Summary
- ✓Final yield and FPY differ by the rework rate; a wide gap means a busy repair bench.
- ✓Reporting both numbers is what turns rework from invisible overhead into a measured loss.