It's a nice problem.

Here:

Given 9 MSD = 10 VSD, hence, 1 MSD = VSD.

Now, to find which division in the MSD crosses the 0 of VSD:

We have 1 VSD = 0.9 MSD

Hence 7 VSD's = 6.3 MSD

Therefore the 0 of the VSD co incides with the 49-6.3 th division = 42.7th division.

Hence, the reading is 42.7 mm or 4.27 cms.