(21)When developing initial margin models and when calculating the appropriate MPOR, counterparties should take into account the need to have models that capture the liquidity of the market, the number of participants in that market and the volume of the relevant OTC derivative contracts. At the same time there is the need to develop a model that both parties can understand, reproduce and on which they can rely to resolve disputes. Therefore counterparties should be allowed to calibrate the model and calculate MPOR dependent only on market conditions, without the need to adjust their estimates to the characteristics of specific counterparties. This in turn implies that counterparties may choose to adopt different models to calculate the amounts of initial margin to be exchanged between them, and that those amounts of initial margin may not be symmetrical.