A vernier caliper have $20$ divisions on the vernier scale which coincide with $19$ divisions on the main scale. The least count of the instrument is $0.1 \mathrm{mm}$. The main scale divisions are of

$1 \mathrm{cm}$ on the main scale of vernier calipers is divided into $10$ equal parts. If $10$ divisions of vernier coincide with $8$ small divisions of the main scale, then the least count of the caliper is