In India the number of labourers i.e. the supply exceeds the demand. Even if some labourers are removed from agriculture the overall agricultural productivity will not be affected. Hence, rural areas experience disguised unemployment.
Now, although the fact is that even if few labourers are removed from agriculture there is no change in production i.e. the marginal productivity of these labourers is zero. But there is no way to determine who is not contributing to production.
There is no systematic and sure way to calculate contribution of each person in the total production.
Hence, it is very difficult to measure rate of disguised unemployment.