When an economy operates at its long-run potential output level,?

The economy is in equilibrium, and the natural and real or actual rates of unemployment will be equal.

In order for an economy to operate at its long-run potential output level, it must be equilibrium, and the economy is balanced in its production. Unemployment is one measure of an economy's equilibrium with the natural and actual rates as two benchmarks rates that must be calibrated towards equilibrium.