Daily mark-to-market occurs if, after the ending of each trading day, the settlement staff of the exchange calculate the settlement price of each futures contract and the profit/loss of each transaction and then adjust the profit/loss of each margin account on that day.
If the net value in a margin account falls below the corresponding margin requirement, the exchange will notify the relevant clearing member, which shall pay additional funds within a time limit to reach the initial margin; otherwise it will not be able to trade on the next trading day.
Daily mark-to-market generally involves the calculations of floating profit/loss and actual profit/loss.