The futures exchange collected HK$479.4 million from brokers yesterday during an intra-day margin call - a risk management exercise aimed at protecting the exchange and maintaining market order during the sharp fall. The futures exchange - a wholly owned subsidiary of Hong Kong Exchanges and Clearing - collected the intra-day margin calls at 11 am after the Hang Seng Index dropped more than 500 points. Within an hour of the margin call being made, all futures brokers deposited money with the exchange to cover possible losses on clients' futures contracts that had not been settled. When an investor trades a futures contract, they must pay brokers an initial margin which will be deposited in a futures exchange bank account. The margin is used to protect the exchange from losses if the clients do not settle their futures contracts. In normal situations, the exchange will only ask futures brokers for more deposits after the market closes. However, in a sharply falling market, deposits are collected during trading hours to ensure there is a sufficient cushion against contract value losses.