| 摘要 |
A method of classifying an item of currency using a currency tester comprises sensing variable characteristics of a currency item and deriving a data vector (X) using values of the sensed characteristics, and transforming the data vector so that the variables represented by at least first and second sets of components (Y1, Y2) of the transformed vector are substantially independent, so that the mahalanobis distance of X is substantially equivalent to the sum of the mahalanobis distances of the components (Y1, Y2), and calculating a mahalanobis distance in at least two parts using said first and second sets of components.
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