Statistical Analysis and Critical Aspects of Surface Measurement using Mechanical Pin-Wheel Machines

The publication of the “Measuring Instruments Directive - MID” (European Directive 2014/32/UE) has determined the inclusion of area measuring machines in the category of legal metrology devices. Leather must follow similar rules for other goods traded by means of a measurement. Finished leathers are usually sold by area and the measurement for verification purposes in commercial trades is regulated by the International Contract No 7 (1998) between the ICT and the ICHSLTA. This contract provides specific indications on commercial issues and defines rules for area checking in case of legal disputes. In general, the contract allows the use of any agreed machine between seller and buyer (mechanical or optoelectronic), but in the event of a dispute it refers exclusively to pin-wheel machines according to ISO 11646 standard. This requirement has been defined without the provision of any technical support and does not consider the deviations of the results using other devices. Furthermore, ICT and ICHSLTA agreed that official controls shall be carried out only in specific Measurement Institutes, among which only 5 around the world have a working instrument, and only one has accredited the test according to ISO/IEC 17025. In this study, 13 small batches of different leather articles were used in an interlaboratory trial that involved 8 participants, including 4 European ICT/ICHSLTA official Measurement Institutes. By means of a statistical analysis of the results, the scope of this study is the identification of critical aspects related to the use of pinwheel machines with particular reference to leather (dimension, deformability, etc) and device characteristics.