Over short periods, the relation between growth in money and growth in nominal income is often hard to see, partly because the relation is less close for short than for long periods, but mostly because it takes time for changes in monetary growth to affect income. And how long a time is itself variable. Today's income growth is not closely related to today's monetary growth; it depends on what has been happening to money in the past. What happens to money today affects what is going to happen to income in the future.