(6)Criteria should be provided to further specify proportional diversification. It is prudent for the Board to limit the exposure to any particular issue or issuer and to make use of different maturities in order to meet its investment objectives. As regards individual issues, commercial paper is issued with an International Securities Identification Number (ISIN) corresponding to the specific investment of the investor (in terms of maturity, amount and other characteristics), so that the investor owns 100 % of the security even if it does not own 100 % of the entire commercial paper programme. This should be taken into account when defining limits to the exposure to a particular issue. In addition, since irrevocable payment commitments may represent a significant share of the total amount of contributions to the Fund, the Board should also consider the collateral pledged to back irrevocable payment commitments when monitoring its overall concentration risk.