There are variation on the theme that could work. This one has the advantage of being simple and fixed, that is, one knows the obligation in advance. The other advantage is the 'comping interest' clause--compound interest being as Milton Friedman has said the "eighth wonder of the world, for the receiver that is--by not starting the clock until the first job it saves lots of $$ and lots of anxiety. All of us appreciated the Givernment role is supporting us. It helped us have a more positive view of government than is evident today.