The first paragraph should discuss what principles were examined and what you learned from the experiment. For each possible source of error given, you must include the approximate magnitude and the direction that it would shift the final result. With these considerations, it can be determined which source of error may have actually contributed to making the experimental value incorrect. I require all students to keep a lab notebook. A large part of my evaluation of your lab performance will be based on spot checks of this book.
Notebooks are an immense help in preparing for lab.
A typical notebook entry will have the experiment number and title at the top of the page as well as the date. A brief outline of procedure will help you organize your time. The next part should be a data table ready to fill in. Leave space for pre-lab lecture notes and possible sources of error. Pages should be numbered sequentially and the first two pages left for a table of contents.