interesting video on Health and Wealth over 200 years

"" (Watch on YouTube)

http://www.youtube.com/watch?v=jbkSRLYSojo

I find the "wealth" axis difficult to comprehend. It seems to me there are many factors to consider (inflation, different costs of living in different places, different currencies and exchange rates). I have an idea of the difference between $400 and $40,000 where I live, but not such a clear idea of what those numbers mean in other parts of the world, or a hundred years ago.