With this clause a datum of price is fixed based on index.
The amount payable to the contractor for the work is adjusted as per increase or decrease of index with respect to the datum index at the time of submission of contract. So with this the price of contract is well balanced for both contractor and owner.
The datum index referred can be for cement, steel, labour, fuel, machinery & other materials with different percentage of the bill amount.
Whenever there is an increase in the prices of any materials by the virtue of the statutory powers by the government, for which there is no provision made in the contract, the burden of such increase will fall on the employer and not on the contractor.