Dear Dr. Purvi Kikani ,

I suggest you to have a look at the following, interesting documents:

- S U R F AC E R O U G H N E S S T E R M I N O L O G Y AN D P AR AM E T E R S

Available at: https://www.predev.com/pdffiles/surface_roughness_terminology_and_parameters.pdf

- Surface Roughness Parameters

Available at: https://www.keyence.com/ss/products/microscope/roughness/line/parameters.jsp

- Topographic characterization of canine teeth using atomic force microscopy images in nano-scale

Negin Beryani Nezafat, Mahmood Ghoranneviss, Seyed Mohammad Elahi, Azizollah Shafiekhani, Zohreh Ghorannevis & Shahram Solaymani

International Nano Letters volume 9, pages 311–315 (2019)

Available at: https://link.springer.com/article/10.1007/s40089-019-00284-8

My best regards, Pierluigi Traverso.

The denominator term (delta_a) is the arithmetic mean of the slope of the surface profile. i.e. it is the arithmetic average of dZ/dX for each point of the profile. For more detail how the average wavelength is defined and calculated, it is probably best to refer to ISO 4287 and 4288.

The average wavelength parameter was developed by Spragg and Whitehouse (https://doi.org/10.1177/002029407200500301). It is a kind of simplification of the autocorrelation analysis to assess the repeatability and dominant wavelengths of a surface. This is of importance for functional surface, but it is dependent on the “function” that the surface is trying to provide. More can be found on this topic in the paper from Spragg and Whitehouse (above) and in the Modern Tribology Handbook - Chapter 2 Surface Roughness Analysis and Measurement Techniques from Bhushan.