Mumbai, Sept. 25 -- Reserve Bank of India (RBI) stated in its latest monthly bulletin that amidst surplus liquidity, the weighted average call rate- the operating target of monetary policy, generally hovered in the lower half of the corridor in August and the first half of September. However, it hardened during September 15-19 as system liquidity moderated on account of tax outflows. Overnight rates in the collateralised segment- the triparty and market repo - and the benchmark secured overnight rupee rate largely moved in tandem with the uncollateralised rate. Yields on three-month treasury bills, certificates of deposit, and commercial papers issued by non-banking financial companies hardened during this period. The average risk premium...