The correct answer is option B: Mean-line and envelop line systems.


The surface roughness of a material is a measure of the irregularities or deviations from the ideal surface. It is important to accurately specify the numerical value of surface roughness in order to ensure the desired quality and functionality of a product.

There are several methods for specifying the numerical value of surface roughness, but not all methods are correct. Let's discuss each option mentioned and understand why option B is not the correct method:

a) Centre-line average (CLA) value:
The Centre-line average (CLA) value is a commonly used method for specifying surface roughness. It involves measuring the vertical deviations of the surface profile from a reference line (usually the mean line) and calculating the average value of these deviations. This method provides a good indication of the average roughness of the surface.

b) Mean-line and envelop line systems:
This option is not the correct method for specifying the numerical value of surface roughness. Mean-line and envelop line systems are not recognized or standardized methods for surface roughness measurement. They do not provide a clear and accurate numerical value for surface roughness.

c) R.M.S value:
Root Mean Square (RMS) value is another commonly used method for specifying surface roughness. It involves calculating the square root of the average of the squared deviations of the surface profile from a reference line. This method provides a measure of the overall roughness of the surface.

d) Peak-to-valley height:
Peak-to-valley height is a method for specifying surface roughness by measuring the vertical distance between the highest peak and lowest valley of the surface profile. This method provides information about the extreme variations in the surface roughness.

In conclusion, the correct method for specifying the numerical value of surface roughness is the Centre-line average (CLA) value, Root Mean Square (RMS) value, or Peak-to-valley height. The mean-line and envelop line systems are not recognized methods and should not be used for surface roughness measurement.