Assertion $A$: If in five complete rotations of the circular scale,the distance travelled on the main scale of the screw gauge is $5 \, mm$ and there are $50$ total divisions on the circular scale,then the least count is $0.001 \, cm$.
Reason $R$: $\text{Least Count} = \frac{\text{Pitch}}{\text{Total divisions on circular scale}}$
In the light of the above statements,choose the most appropriate answer from the options given below:

• A
  Both $A$ and $R$ are correct and $R$ is the correct explanation of $A$.
• B
  $A$ is not correct but $R$ is correct.
• C
  Both $A$ and $R$ are correct and $R$ is $NOT$ the correct explanation of $A$.
• D
  $A$ is correct but $R$ is not correct.