A margin call is the worst enemy of an operator. Unfortunately, this happens to many operators, some because they used technical poor administration of the capital (orwithout using any technique) and other operators happens because they don't evenknow what is a margin call.
A margin call occurs when capital in your account falls below the maintenance margin (which is equal to the capital required to open a transaction, e.g. $250 if you use 400:1 or $1,000 if you use 100:1 in standard operations). Here's an explanatory table:

