2.3 In addition to detailed sharing mechanisms covering specific aspects of the partnership, National Savings is entitled to receive 50 per cent of the amount by which SBS's overall net profit margin exceeds an agreed percentage in the contract but will not share in any losses. SBS expects a profit margin equivalent to 8.7 per cent a year over the life of the contract (based on 15 years). The calculation of any excess profit will be on an annual basis, after deduction of any amounts receivable by National Savings under other sharing arrangements.