A fund manager buys a gold futures contract at $1000 per troy ounce, each contract...

The most loss the fund manager can bear without facing a margin call is the loss that will make his margin balance account no lower than $4,000. This means he can have a loss of upto $1,000 before a margin call is triggered, implying that prices can fall by $10 per ounce (=$1,000/100 ounces per contract) without triggering a margin call. The margin call will be to top the margin up to the $5,000 initial margin.