Seminar, three hours; discussion, three hours. Limited to departmental graduate students. Many graduate students have had little practice in making rough estimates or order of magnitude (OOM) assessments of physical problems, and even less practice at talking through problems with others. One key problem is tendency for rote memorization to take precedence over understanding. Discussion of basic problems from OOM perspective, with focus on problems appropriate to Earth, planetary, and space sciences, to inculcate physically based reasoning and promote effective on-your-feet communication. Attendance at departmental colloquium required each week. S/U or letter grading.