There are two main approaches that can be used by clearing houses, with regards to how they make their margin calls. The first approach is using variation margin only. If the value of the margin account falls below the initial margin level, that counterparty will be required to top it back up to the initial margin level. This is the approach used by the London Clearinghouse, or LCH. The maintenance margin approach requires that a counterparty only top up their margin account if it drops below the maintenance margin level, which is set below the initial margin level. The result of this is that for smaller losses, reducing the margin account below the initial margin level, but not below the maintenance margin level, will not require money to be paid in by that counterparty. But only if the loss suffered by the counterparty gets down below the maintenance margin level, would they be required to top their margin account back up to the initial margin level. This is the approach used by the Chicago Mercantile Exchange clearing house, or the CME.