The above problem appeared in JEE- Advanced 2014 paper-1. Please try it before joining the discussion.
The answer given in the official key, and everywhere else is \(4\). Here is a solution:
But I believe that the answer should be \(8\). In the solutions released by coaching institutes, they have made an unsubstantiated assumption that the maximum error in measuring the length is equal to \(1\) Least count of the Vernier scale. I think this is wrong. The problem clearly states that two independent observations are made. This must imply that the maximum error in each observation is \(1\) least count. And hence, it follows that the maximum error in the difference of the readings is two least counts.