The roughness profile of a surface is depicted below.

The surface roughness parameter $${R_a}\,\,$$ (in $$\mu m$$) is ________________.

In an interchangeable assembly, shafts of size $${25.000^{\matrix{ { + 0.040} \cr { - 0.010} \cr } }}\,\,mm$$ mate with holes of size $${25.000^{\matrix{ { + 0.030} \cr { + 0.020} \cr } }}\,\,mm.$$

The maximum interference (in microns) in the assembly is

The geometric tolerance that does not need a datum for its specification is

Which one of the Instrument is a comparator