interpretation and relevance of Ra multiple decimal digits

Valentin Nelea posted on Fri, Nov 29 2013 10:55 PM

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Hi,

I have a question about the interpretation and relevance of multiple decimal digits of Ra as calculated and reported by AFM softwares.

If the best resolution (the vertical one) of a common AFM (NanoScopeIII from DI for example) is 0.1 nm, why Ra values are reported with two or more decimal digits.

For example, a measurement got Ra=1.233 nm. This does not mean that surfaces of which calculated Ra are numbers like 1.2xx have not all in reality the same roughness, i.e. Ra=1.2 nm, with the measurement precision limitated by the instrument resolution.

Thank you.

Valentin