130 THE WORK OF THE STOCK EXCHANGE 
frequently, while some stocks are rising others are declining. 
Thus it is quite possible for the customer’s debit balance to be 
increased at the same time by rising prices on his short stock 
and declining prices on his long stock. If meanwhile his debit 
balance had been reduced by fully crediting against it the 
market value of the short stock, his unhappy broker might 
under the circumstances have to be prompt to call for more 
margin in order to save himself from serious loss. 
The Margin Card.—A current record of Blank’s equity in 
his account—or his “margin,” -as it is more often called—is 
constantly kept by the margin clerk of the brokerage house. 
The broader economic significance of margins has already been 
discussed in a previous chapter.’ The margin clerk keeps a 
separate record for every customer of his house, and constantly 
adjusts the customers’ margins as the trend of security prices 
dictates. In this way the commission house is always in touch 
with the amount of margin maintained by each of its cus- 
tomers, and in a position to call the given customer for more 
margin, or to know whether he can safely make new transac- 
tions on the basis of his existing margin. The margin cards 
used by different Stock Exchange commission houses differ 
more or less in their details. Figure 57 represents a form of 
margin card easy for the layman to understand; it cannot be 
said, however, that this particular form is typical of margin 
cards generally employed. The items which it contains show 
the condition of Mr. Blank’s margin at the time when his 
monthly statement above included was issued. It will be noted 
that the securities which the customer originally owned out- 
right, but which he deposited as margin, are entered exactly 
like the securities which he subsequently bought on margin. 
At the top of the margin card, the customer’s debit or credit 
balance, and the market value of his long and short stock are 
entered. These figures, as well as the margin derived from 
2 See Chapter VII, p. 184.