In practice, measurement results are sometimes described by an estimate, which is not the best one as defined in the GUM. Such alternative estimates arise when the result of a measurement is not corrected for all systematic effects. No recommendation exists in the GUM for associating an uncertainty with an uncorrected estimate.

A common choice in guidelines and in the literature is the uncertainty u(y)=u2(y)+(y-y)2u\left( {y'} \right) = \sqrt {{u^2}\left( y \right) + {{\left( {y - y'} \right)}^2}} for an alternative estimate y′. It arises from the expected quadratic loss, on which, also in the GUM, the standard uncertainty u(y), and the best estimate y are based. However, such an uncertainty is not a standard uncertainty and we establish, it may not be used for uncertainty propagation.

One consequence is, for example, that pairs (y′, u(y′)) are not to be used in calibration certificates.

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Engineering, Electrical Engineering, Control Engineering, Metrology and Testing