Vernier constant is defined as the difference between the value of one main scale division and one vernier scale division. It is also known as the least count of vernier calliper.

The main scale division of the given vernier calliper is $MSD=\frac{1 \mathrm{cm}}{20}=0.5 \mathrm{mm}$.

$LC=\frac{MSD}{n}=\frac{0.5 \mathrm{mm}}{10}=0.05 \mathrm{mm}=5\times {10}^{-2} \mathrm{mm}$