Taguchi suggests the transformation of the repetition data
in a trial into a consolidated single value called the S/N ratio.
Here, the term ‘signal’ represents the desirable value (mean)
and the ‘noise’ represents the undesirable value (standard
deviation). So the S/N ratio represents the amount of variation
present in the quality characteristic. Depending upon
the objective of quality characteristic there can be various
types of S/N ratios. Here the desirable objectives are lower
values of surface roughness and force components. So the
lower-the-better type S/N ratio, as given below was applied
for transforming the observed data: