Table 3.

Parameters of 3D surface topography according to ISO 25178.

	Description	Equation
Sa (µm)	Arithmetic mean surface height	$S_a=\frac{1}{m\times n}\underset{0}{\overset{m}{{\displaystyle \int }}}\underset{0}{\overset{n}{{\displaystyle \int }}}\left|Z\left(x,y\right)\right|dxdy$	(2)
Sz (µm)	Maximum height, between the highest peak and the deepest valley	$S_z=Sp-Sv$	(3)
Ssk	Surface skewness (dimensionless)	$S_{sk}=\frac{1}{m\times n\times S_q^3}\underset{0}{\overset{m}{{\displaystyle \int }}}\underset{0}{\overset{n}{{\displaystyle \int }}}Z{\left(x,y\right)}^{3}dxdy$	(4)
Sku	Surface kurtosis (dimensionless)	$S_{ku}=\frac{1}{m\times n\times S_q^4}\underset{0}{\overset{m}{{\displaystyle \int }}}\underset{0}{\overset{n}{{\displaystyle \int }}}Z{\left(x,y\right)}^{4}dxdy$	(5)