To illustrate a simple but often ignored concept – what is the estimated total cost of the following?
||what is the total plus-minus range?
I say the answer is:
Notice that the plus-minus range for the total cost is less than the sum of the plus-minus ranges. This will always be true when adding in quadrature.
Uncertainty Analysis Reference
In accordance with the rules of quadrature, our uncertainty is:
Of course, no more than 2 significant digits are warranted here; therefore
The quantities alpha, beta, and gamma must have uncertainties which are uncorrelated and random.
If say same-cost items were considered, with a constant percent plus-minus cost:
items of the same cost
(but still independent variables) were considered, with a constant
) plus-minus cost:
Here the plus-minus range for the total cost,
percent, is much less than
If items of a random cost (and still independent variables) were considered, with a constant percent () plus-minus cost, we might calculate percent instead of percent.