Which one of the following statements is TRUE?

Holes of diameter $${25.0^{\matrix{ { + 0.040} \cr { + 0.020} \cr } }}\,\,mm$$ are assembled interchangeably with the pins of diameter $${25.0^{\matrix{ { + 0.005} \cr { + 0.008} \cr } }}\,\,mm.$$

The minimum clearance in the assembly will be

The flatness of a machine bed can be measured using

Which one of the following instruments is widely used to check and calibrate geometric features of machine tools during their assembly?