Transparent ratios
Unit concentration = target-unit events ÷ all comparable events
NFF share = no-fault-found outcomes ÷ shop returns
Recurrence after swap = repeat symptoms ÷ swaps with follow-up
Interpretation boundary
A target unit may have more exposure, and an NFF outcome may reflect test coverage, context loss, or a truly healthy component. Recurrence after a swap may implicate installation context or may only expose inconsistent follow-up. The three percentages are review triggers, not diagnoses.
Use serial and context history
Review installations, configuration, wiring and connectors, original event evidence, test conditions, and previous actions. Apply consequence and regulatory obligations independently of the selected percentage threshold.