A question about significant digits of digits in parentheses at the end

[swampwiz]

I was looking at the value of Avogadro's number

6. 022 141 29(27)×10²³

and was trying to figure out what exactly is meant by the parentheses at the end. I'll take a guess and say that the best determined value has these digits, but that the error is high enough so that only by using the number before the parentheses, with its default error of being +/- 1/2 of the value of the last digit place (i.e., here .000 000 01×10²³) can the proper number of significant digits be preserved.

Obviously, the most descriptive value would be the one that has the exact amount of uncertainty, but it is not presented here.

 

[torquil]

It means 6.022 141 29 * 10^23 +/- 0.000 000 27 * 10^23