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Before sentencing you meet up with a probation officer. That title is a bit misleading. Their job at this point has nothing to do with probation. They write up a report which is supposed to be a comprehensive profile of you. Make sure you have your lawyer present during this interview.
Lawyers cost a lot. If you cannot afford one, your best bet is to study up yourself. This is good advice even if you must rely on the public defender. Buy a couple of the great books such as The Prisoners Self Help Litigation Manual. You should also pick up Federal Sentencing Guidelines, as well as Federal Criminal Codes and Rules. You got to lean the rules of the game before you can play ball.