A Theory of Measurement Uncertainty Based on Conditional Probability
  A theory of measurement uncertainty is presented, which, since it is based exclusively on the Bayesian approach and on the subjective concept of conditional probability, is applicable in the most general cases.   The recent International Organization for Standardization (ISO) recommendation on measurement uncertainty is reobtained as the limit case in which linearization is meaningful and one is interested only in the best estimates of the quantities and in their variances. 
G. D'Agostini