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2

The definition of Ampere is obtained by the below equation of force between two infinitely long parallel current carrying conductors. Where $F$ is force, $\triangle{L}$ is small length element, $\mu_0$ is absolute permeability of vaccum or free space, $I_1, I_2$ are current flowing through two conductors. By calculation we can obtain that ...

2

NIST has its own more sophisticated guidelines for reporting uncertainty of measurments. http://physics.nist.gov/Pubs/guidelines/TN1297/tn1297s.pdf There is nothing wrong with reporting two digits in an uncertainity, and many peer reviewed journal articles do. This is especially true when the first digit of the uncertainity is 1. If you report +/-1, 1 ...

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First, can it be written as the following? $$N_A=6.022\,141\,29\times10^{23}\pm0.000\,000\,27\times10^{23} {\rm mol}^{-1}$$ Yes. A cleaner way to write it is $$N_A=6.022\,141\,29(27)\times10^{23}{\rm mol}^{-1}$$ where the $(27)$ indicated the uncertainty in the last $N$ digits (where $N$ is the number of digits inside the parenthesis). If I have a ...

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