Evolving-coefficient braking index ($n=q+(\Omega /\dot{\Omega })(\dot{K}/K)$)

For $\dot{\Omega }=-K(t){\Omega }^q$, differentiation gives the displayed braking index. Inferring the torque power $q$ from a measured index therefore requires an effectively constant coefficient. Field evolution, changing inclination and moment-of-inertia changes can all contribute to the difference.