  The aim here is to address the origins of sustainability for the real growth
rate in the United States. For over a century of observations on the real GDP
per capita of the United States a sustainable two percent growth rate has been
observed. To find an explanation for this observation I consider the impact of
utility preferences and the effect of mobility of labor \& capital on every
provided measurement. Mobility of labor results in heterogenous rates of
increase in prices which is called Baumol's cost disease phenomenon.
Heterogeneous rates of inflation then make it impossible to define an invariant
measure for the real growth rate. Paradoxical and ambiguous results already
have been observed when different measurements provided by the World Bank have
been compared with the ones from the systems of national accounts (SNA). Such
ambiguity is currently being discussed in economy. I define a toy model for
caring out measurements in order to state that this ambiguity can be very
significant. I provide examples in which GDP expands 5 folds while measurements
percept an expansion around 2 folds. Violation of invariance of the
measurements leads to state that it is hard to compare the growth rate of GDP
for a smooth growing country such as the U.S. with a fast growing country such
as China. Besides, I state that to extrapolate the time that economy of China
passes the economy of the US we need to consider local metric of the central
banks of both countries. Finally I conclude that it is our method of
measurements that leads us to percept the sustainable growth rate.
