An equilibrium flow claim is a pair of checked directed ledgers. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Detailed balance compares opposing flows
Both directed flows are six in the accepted case.
ΦA→B=6,ΦB→A=6
Equal flows accept the balance claim
The accepted bit is one only because the flows match.