# Uncertainty writing

This will sound like a silly question, but I don't recall that my professors ever though me what this means. For example:

X=1.2345(6) units

This is uncertainty, that much I do know, but does it mean:

X=(1.2345+-0.0006) units or??

We only did the second notation, and recently (mostly in particle physics papers) I'm finding this notation, and I have problems with it :\

Sorry if it's a silly question...

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Yes, the notation $$abcd.efgh(jkl)$$ means $$(abcd.efgh\pm 0.0jkl)$$ where the number of "plus minus" digits of the mean value corrected by the error margin is the same as the number of digits written in the parentheses, in my case three (in other words, both the mean value and the error margin have the same number of digits following the decimal point). You did it right in your example, too.

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Thank you! I wasn't really sure if I'm interpreting it right :) I'll accept your answer in 2 minutes, since I cannot do that atm xD –  dingo_d Nov 24 '12 at 8:11
And don't forget, the error margin is a standard deviation, not a maximal error. –  Arnold Neumaier Nov 24 '12 at 16:38