To work out the doubling time of an annual percentage growth, divide it into 70. Why 70? It is 100 × ln(2). So, for example, when electric power consumption was growing at 7% a year, we had to come up with double the generating capacity every decade. Further, every decade consumed more power than in all previous history combined. These are the consequences of simple arithmetic.~ Roedy (1948-02-04 age:70) see lecture by Dr. Albert A. Bartlett.