Comments on ‘‘Combined measurements – A way to improve the measurement accuracy of an additive quantity’’ by R. Siuda and A. Grabowski Józef Wiora ⇑ , Andrzej Kozyra, Alicja Wiora Institute of Automatic Control, Silesian University of Technology, ul. Akademicka 16, 44-100 Gliwice, Poland article info Article history: Received 19 October 2012 Received in revised form 13 November 2012 Accepted 19 November 2012 Available online 13 December 2012 Keywords: Measurement uncertainty Correlation Type B evaluation abstract The commented article has introduced to metrology a new way of lowering the uncertainty assessed using Type B evaluation. The proposed method operates properly under some assumptions but unfortunately, the idea has been presented with some understatements and mistakes. The weak points are shown and discussed in this article. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Siuda and Grabowski recently proposed a very interest- ing method to improve measurement uncertainty of an additive quantity, named as the combined measurement method (CMM) [1]. The physical observable quantity is said to be additive when a measurand of several joined ob- jects is equal to the sum of the measurands of those indi- vidual objects [2]. Authors proved that they found a solution to improve measurement uncertainties assessed using Type B evaluation. The uncertainty is lowered thanks to a performance of additional measurements – apart from the measurements made for each object, there is also a need for additional measurements for couples and triples (and so on) of the objects. Applying the least squares opti- misation, measurement values are calculated and deter- mined with better uncertainties than those obtained from direct readouts of each of the objects separately. 2. Remarks The idea of CMM is very interesting, especially for read- ers dealing with practical measurements of additive quan- tities, such as mass, length and resistance, because it is a unique method to lower the Type B uncertainty without the need for better measuring equipment. However, the paper includes some statements that require supplemen- tary remarks and we enumerate them bellow. 2.1. Non-conformant arguments of matrices Eq. (1) in the commented paper [1] is incorrect for two reasons: 1. the transpositions are written incorrectly – non-confor- mant arguments of the multiplication; 2. even if it was written as: p ¼ Kx ð1Þ the notation would be true only in the case of the absence of measurement errors. 0263-2241/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.measurement.2012.11.022 ⇑ Corresponding author. E-mail address: jozef.wiora@polsl.pl (J. Wiora). Measurement 46 (2013) 2259–2261 Contents lists available at SciVerse ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement