Equation 4 · Part 6 · Comparing the Main Approaches to Scientific Instruments and Metrology

Symbol x_i

u_c^2(y) = \sum_{i=1}^{N} \left( \frac{\partial f}{\partial x_i} \right)^2 u^2(x_i)

x_i

What this part means

$x_i$ occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.

Its job in the formula

$x_i$ occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.

Full expressionSymbol x_iArticle meaning

The passage around this formula

Uncertainty itself has a standard grammar, laid out in the GUM and adopted domestically by NIST in Technical Note 1297. Every source of doubt about a measured value is classified as either a Type A evaluation — estimated from the statistical scatter of repeated observations — or a Type B evaluation — estimated from any other information, such as a calibration certificate, a manufacturer’s specification, or physical reasoning about a known systematic effect [ 2 ] [ 3 ] . These component uncertainties are combined, following an explicit propagation rule, into a combined standard uncertainty, which is then multiplied by a coverage factor (conventionally k=2 , corresponding loosely to a 95%…

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Learn the underlying idea

A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

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Sources cited in the surrounding passage

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