Abstract
To judge the quality of surface roughness specimens two criteria are particularly important: the deviation of the mean value from the nominal value, and the scatter within the specimens. These criteria may be read very easily, and without any mathematical expedients, from graphs on probability paper. The practical use of probability paper is explained.
From the evaluation of the results it is seen that the behaviour of certain instruments is such that the influence of instrument cut-off is contradictory to the theory and the opposite of the behaviour of other instruments. An attempt is made to explain this phenomenon, and an extension to the relevant standards is proposed which would ensure that all instruments conforming to the same standard would also yield the same results.
Finally, possible methods are mentioned which would enable instruments to be checked in these respects, in order to ascertain whether they possess the required characteristics.
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