sharp limit on price movements of a share of more than 10–15%; restrictions and institutional barriers to short-selling by domestic and international traders; frequent adjustments of margin requirements in response to changes in volatility; strict guidelines on mutual fund redemptions; and actions of the Ministry of Finance to control the total shares of stock and exert moral suasion on the securities industry. An example of the latter occurred when the ministry invited representatives of the four largest securities firms to tea in the early afternoon of the day of the crash. After tea at the ministry, these firms began to make large purchases of stock in Nippon Telegraph and Telephone. Hong Kong The worst decline among world markets was in Hong Kong, with a drop of 45.8%. In its biggest-ever single fall, the Hang Seng Index of the Hong Kong Stock Exchange dropped 420.81 points on Black Monday, eliminating HK$65 billion' (10%) of the value of its shares. Noting the continued fall of New York markets on their next trading day, and fearing steep drops or even total collapse of their own exchanges, in Hong Kong the Stock Exchange Committee and the committee of the Futures Exchange announced the following morning that both markets would be closed. Their closure lasted for four working days. Their decision was motivated in part by the very real possibility that market collapse could have extremely serious consequences for the entire financial system of Hong Kong, perhaps resulting in rioting in the streets, with the added threat of intervention by the army of the People's Republic of China. According to Neil Gunningham, a further motivation for the closures was brought on by a significant conflict of interest: many of these committee members were themselves futures brokers, and their firms were in danger of substantial defaults from their clients. Although the stock exchange was in distress, structural flaws in the futures exchange, which was then world's most heavily traded outside the U.S., were at the heart of the greater financial crisis. The structure of the Hong Kong Futures Exchange differed greatly from many other exchanges around the world. In many countries, large institutional investors dominate the market. Their principal motivation for futures transactions is hedging. In Hong Kong, the market itself, as well as many of its traders and brokers, was inexperienced. It was composed heavily of small, local investors who were relatively uninformed and unsophisticated,