I use this in my 10th/11th grade Chemistry class as an introduction to Dimensional Analysis. I tried it for the first time last year and the students have seemed to retain the information more as a result. The document is used in cooperative learning groups and they are given 2 dimensional analysis problems to peruse. They are asked questions relating to how a problem starts and ends, how units are arranged, how the top unit is related to the bottom unit in a conversion factor. It takes 10 to 15 mintues of class time for the groups to work on it . Then I launch into Dimensional Analysis.