A vernier callipers has a main scale marked every 0.5 mm…

Step 1. One vernier division $= \dfrac{24 \times 0.5\ \text{mm}}{25} = 0.48\ \text{mm}$.

Step 2. Least count $= 0.5\ \text{mm} - 0.48\ \text{mm} = 0.02\ \text{mm}$, the same as $\dfrac{0.5\ \text{mm}}{25}$.

Step 3. $0.02\ \text{mm} = 0.002\ \text{cm}$.