Two measurements, two jobs
Suppose an illustrative workshop sells one hundred identical items for ten dollars each, then sells the same quantity for eleven dollars each. Its sales rise from one thousand to eleven hundred dollars. The quantity has not risen. This deliberately simple example shows why a dollar total alone cannot identify a change in physical output.
The Bureau of Economic Analysis recommends current-dollar measures for showing the size of economic activity or comparing output and spending at a point in time. These measures retain the prices associated with the period. They answer a useful question, but a different one from how much output changed.
Sources: s1
For change through time, inspect the real series
BEA recommends real measures when examining changes in output or spending over time. Its chain-type indexes and chained-dollar measures remove effects of price changes. The agency notes that their percentage changes match, allowing either form to express the corresponding growth comparison.
For a chart, retain the series name, units, frequency, seasonal treatment and release vintage. Check whether a displayed rate compares quarters, years or an annualized quarter. A correctly copied percentage can still answer the wrong question if its interval and price basis disappear from the caption.
Return to the official series
An economy contains changing products, services and relative prices, so official real GDP is more involved than counting identical workshop items. Nor does output growth alone describe distribution or every aspect of well-being. Use the hypothetical calculation to understand the distinction, then use the documented official series for an empirical claim.