Correct option is A
Slip gauges (gauge blocks) are precision instruments used for accurate measurement and calibration of dimensions. They are manufactured to very high accuracy and are used in metrology laboratories and workshops. These gauges are specified in units of length, typically in millimetres (mm) or sometimes inches.
Each slip gauge has a precisely known dimension, and by combining multiple gauges (wringing), exact lengths can be built. They are not related to force, weight, or distance measurement over large scales, so units like kilograms, newtons, or kilometres are not applicable.
