Oh, thanks. If one doesn’t learn something new every day, one might as well lie down and die!
When I first saw the graph of Opium shipments into China, I too thought "Logarithmic." And while I was looking up the spread of disease (because in my argument, I was likening the spread of drug addiction to the spread of disease), I found that they routinely referred to the exponential rate of infection as a "logistical growth curve", and so I looked it up. I've been using it ever since.
I too like to learn new things whenever I can. :)