6.33 This is a key part of the contract and the NHSScotland body should consider the degree to which returned bids comply with the payment mechanism set out in the ITPD. An assessment should be made of the strength and likelihood of any suggested system of performance deductions in variant bids which vary from the one prescribed by the NHSScotland body in the ITPD. If any payments are volume related, the NHSScotland body should consider both the maximum amount that may be payable and the base case position. A robust calibration model is fundamental to agreement, acceptance and understanding of the payment mechanism.