$\mathrm{Assertion} A:$ If in five complete rotations of the circular scale, the distance travelled on the main scale of the screw gauge is $5 \mathrm{mm}$ and there are $50$ total divisions on a circular scale, then the least count is $0.001 \mathrm{cm}.$

$\mathrm{Reason} R:$
Least Count $=\frac{\text{ Pitch }}{\text{ Total divisions on circular scale }}$
In the light of the above statements, choose the most appropriate answer from the options given below.

• Correct answer
  A

  $A$ is not correct but $R$ is correct.
• B

  Both $A$ and $R$ are correct and $R$ is the correct explanation of $A.$
• C

  $A$ is correct but $R$ is not correct.
• D

  Both $A$ and $R$ are correct and $R$ is NOT the correct explanation of $A.$

Hence, the correct answer is option: 'A'.