Thermometer Accuracy

In my differential equations class, students ran an experiment on the accuracy of a nondigital thermometer.  Most directions for use of nondigital thermometers say to leave under the tongue for 2 minutes, so students tested the accuracy of this.   Three groups performed different activities for two minutes (cheweing gum (placebo group), jumping jacks, and drinking a cold refreshing beverage).  Students collected temperature readings every 30 seconds for 4 minutes.  Data was run through Logger Pro, and students analyzed data using best fit lines.  They then compared their best fit line to the differential equation that models this situation (Newton's Law of Cooling).  Each group found that it took about 3-4 minutes for the thermometer to stabilize.  Through this experiment, I found several issues in the students' lab reports.  Students didn't include information that I requested, did not include their data set in their final report, and used wrong data points to solve their differential equation.  So, in spring, I plan to rewrite the directions for this activity (original one is attached) and redo the lab.