Hi David,


i link here because here you explicit your thought.
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Not smoking anything my friend... those rules were drilled into my psyche during the 6 years I spend at the University of Missouri-Rolla studying nuclear engineering and computer science. It's a pretty fundamental rule about significant digits in calculations. 3.1 is not the same as 3.1000. Every number written has an implicit error of ± 1/2 the last significant digit. So 3.1 * 2.5567 is 7.9 ± 0.05. 3.1000 * 2.5567 is 7.9258 ± 0.00005. You need to forget the way your grade school teacher taught you to do arithmetic. *g*

1. point
>Every number written has an implicit error of ± 1/2 the last significant digit.

Then you cannot write a exact number ( 1 is 1 ± 0.5, 1.0 is 1.0 ± 0.05 .... )
because you must write infinite decimal digits.

But exist conventions !

If I say that 3.1 are exactly 3.1 then it is like writing 3.100000000000000000....

3.1 is exactly 3.1000000000000000000000000000000000......
7.9258 is exactly 7.92580000000000000000000000.......

2. point

For 3.1 * 2.5567, if 3.1 is 3.1 ± 0.05, also 2.5567 is 2.5567 ± 0.00005,
and the result is 7.92577 ± 0.1279925.

You use measure * factor ( the reason is a mystery )
But however, on this case :

(3.1 ± 0.05) * 2.5567 is 7.92577 ± 0.127835.

You are merging the
theory of the measure with the theory of the calculation,
but with a personal arbitrary arithmetic.

Here, we are alone dealing the theory of the calculation,
we are not measuring any physical event.

Here we have only two factors.

Fabio