Which of the following is the most precise device for measuring length?

  • A
    $A$ vernier callipers with $20$ divisions on the sliding scale.
  • B
    $A$ screw gauge of pitch $1 \, mm$ and $100$ divisions on the circular scale.
  • C
    An optical instrument that can measure length to within a wavelength of light.
  • D
    Precision cannot be changed by changing the instrument.

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