Quarterly delta determining posture. Measure: current quarter corroboration count, parametric recall rate, citation coverage vs prior quarter. Positive delta = defended (above equilibrium). Negative delta = contested (below equilibrium, maintenance lapsed). Calculate per perimeter. Document in engagement record. Positive rate enables compounding, negative rate signals forfeiture. Use for: posture determination, maintenance effectiveness measurement, forfeiture detection. Measure quarterly — annual insufficient. Schema entropy rate is the operational defense line metric. Makes contested posture visible.