Mutual deposits on a contract. In any contract on an exchange either broker party to it may call
at any time during the continuance of it for a mutual deposit (a deposit by both) of (usually) 10 per
cent. If the market price of the security or commodity covered by the contract changes so as to
reduce the margin of either party below 5 per cent the other party may demand a restoration of
the impaired margin to 10 per cent. This demand may be repeated as often as the margin is
reduced.