Right, extrapolation from the present and past where the growth has been exponential is not promising. But if somehow know the saturation level, upper asymptot

Right, extrapolation from the present and past where the growth has been exponential is not promising. But if somehow know the saturation level, upper asymptote, then what are doing is more like interpolation than extrapolation. Then the sigmoid curve is the solution to the differential equation I posted here a few minutes ago here at https://news.ycombinator.com/item?id=31429475 https://news.ycombinator.com/item?id=31429475 and there is just the one free parameter k. Sometimes in practice have a shot at estimating k.