h-bar limits measurement precision. What limit arises for h-bar itself?

Question

The question is simple.

h-bar, or $\hbar$, limits the precision of every measurement, books tell us. For example, length measurements are limited by the Compton wavelength.

What limit for the measurement of h-bar itself arises? Or is there no such limit?

Answer 1

There is no uncertainty at all in the value of $\hbar$. In the 2019 revision of SI units, Planck's constant was defined to be exactly $6.62607015 \times 10^{-34}$ Joule seconds.