David,

It was vary long time ago I stadied this stuff so I may be wrong but doesn't implicit errors compound when you do arithmetichs with such numbers?

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>And none of this changes the fact that when these numbers are stored in a binary computer with a fixed number of bits that additional errors are going to be introduced.
>
>3.1 ± 0.05 * 2.5567 ± 0.00005 is 7.9 ± 0.05.
>3.1000 ± 0.00005 * 2.5567 ± 0.00005 is 7.9258 ± 0.00005
>
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