Schuld II

(...) Another significant aspect was that the debt service depended on how much the German economy could afford to pay, taking the country’s reconstruction and the export revenues into account. The debt service/export revenue ratio was not to exceed 5%. This meant that West Germany was not to use more than one twentieth of its export revenues to pay its debt. In fact it never used more than 4.2% (except once in 1959). In any case, since a large portion of the German debts were paid in deutsche marks, the German central bank could issue money, or in other words monetise the debt.
Another exceptional measure was that interest rates were substantially reduced (between 0 and 5%).

Daqui.