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Equation 4 · Part 2 · Comparing the Main Approaches to Scientific Instruments and Metrology

Symbol y

uc2(y)=∑i=1N(∂f∂xi)2u2(xi)u_c^2(y) = \sum_{i=1}^{N} \left( \frac{\partial f}{\partial x_i} \right)^2 u^2(x_i)
yy

What this part means

y is an argument of the function-like quantity on the left; its role is set by that function’s stated inputs.

Its job in the formula

y is an argument of the function-like quantity on the left; its role is set by that function’s stated inputs.

The passage around this formula

…is quoted without an accompanying uncertainty, the number cannot be compared against another laboratory’s figure, however precise the instrument sounds. The combined standard uncertainty uc(y)u_c(y) for a measured quantity y = f(x1x_1, x2x_2, …\ldots, xNx_N) that is a function of several independently uncertain inputs is, to first order, uc2(y)=∑i=1N(∂f∂xi)2u2(xi)u_c^2(y) = \sum_{i=1}^{N} \left( \frac{\partial f}{\partial x_i} \right)^2 u^2(x_i). which is the law of propagation of uncertainty the GUM formalizes [ 2 ] . This equation matters here because it is the reason a headline resolution figure for any of…

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Learn the underlying idea

A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.

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Sources cited in the surrounding passage

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