Here you go, an actual example of your ‘rule of 70’ at work.
”Rule of 70 Versus Real Growth It's important to remember that the rule of 70 is an estimate based on forecasted growth rates. If the rates of growth fluctuate, the original calculation may prove inaccurate. The population of the United States was estimated at 161 million in 1953, approximately doubling to 321 million in 2015. In 1953, the growth rate was listed as 1.66%. By the rule of 70, the population would have doubled by 1995. However, changes to the growth rate lowered the average rate, making the rule of 70 calculation inaccurate.”
