Conventionally, fiscal policy analysis makes a distinction between "discretionary" budget changes and "built-in stability". This distinction is the first step to defining a structural budget balance operationally. Budget deficits vary automatically with the business cycle. Revenues automatically rise as the economy expands; unemployment transfers are reduced, leaving a deficit or surplus at the cyclical peak which may be termed a "structural" budget balance. The "built-in stabilizer" component of the deficit should be self-cancelling as the cyclical output gap is closed so that it is temporary and non-structural. A structural budget deficit is then that excess of public spending over revenues which would persist if the economy were to grow steadily at its highest sustainable employment rate, i.e. at the same rate as potential output.