The 3D film Avatar is apparently doing well at the box office. Its $1.3bn sales to date put it in contention with the record holder Titanic (1997), at $1.8bn, and eclipse Gone With The Wind (1939), which managed $390m.
Or so the publicity tells us. But for anyone with an ounce of numeracy, this is nonsense. Adjusted for US inflation, Titanic's sales were $2.4bn and Gone With The Wind's getting on for $6bn. Add another pinch of numeracy and a further thought occurs.
Inflation apart, real incomes rise over time. If a thing cost $10 in 1900, the question is not just what it would cost today, but what it cost then in terms of available resources.