510 Part V: Index Options and Futures 
If he continued to hold the contract until expiration, this process of adding his 
daily gain or subtracting his daily loss from the account would recur each day. Finally, 
on the last day, the futures contract is deemed to close at the exact opening price of 
the S&P 500 Index and the variation margin is calculated again at that price. Then 
the futures contract is expired, so it is "erased" from his account. He is then left with 
only the cash that he made or lost on the trade of his contract. 
The leverage produced by small margin requirements (as a percent of the total 
value of the contract) is a major factor in making futures very volatile, in dollar terms. 
In the preceding example, a $30,000 margin investment controls $351,250 worth of 
stocks. Due to their volatility, many futures contracts trade with a limit. That is, the 
price can only fluctuate a fixed amount above or below the previous day's closing 
price. This concept is intended to prevent traders with large positions from being 
able to manipulate the market drastically in either direction. 
S&P and NYSE Expiration. S&P 500 futures expiration occurs in a some­
what complex way, compared to those indices whose options and futures expire 
at the last sale on the final day of trading. Some years ago, in order to attempt 
to reduce the volatility that index futures and options expiration was causing in 
the stock market, the NYSE and the Chicago Mercantile Exchange (where the 
S&P 500 futures trade) agreed to change the expiration of their index products 
from the end of trading on the last Friday to the morning of that day. The effect 
of expiration on the stock market is discussed in the next chapter. 
As a result, the S&P futures and futures options as well as futures, futures 
options, and index options on the New York Stock Exchange Index settle in the fol­
lowing manner on their last day of trading. On expiration day - the third Friday of 
the month - the "final" price for purposes of settling futures and options is comprised 
of taking the opening trade of each stock and calculating an index price based on 
those opening prices. There is no actual trading in the futures and options on that last 
Friday; they cease trading at the close of trading on the previous day, Thursday. 
The purpose of this change was to give the specialists on the New York Stock 
Exchange more time to line up the other side of trades to handle order imbalances. 
Under the new rules, index arbitrageurs are forced to enter their buy or sell orders 
as market on open orders on that last Friday before 9 am EST. The specialist can then 
take his time in opening the stock if he needs to; he can solicit orders if there is too 
much stock to buy or sell. 
The effect of all this is that the "final" index price for settlement purposes is not 
known until all the stocks in the index have opened. It may take some time to open 
all 500 stocks in the S&P 500 Index if there is a volatile market that Friday morning