A journal is any notebook in which you record what data you collect.  You can keep a journal for any purpose. It can be a record of your progress with whichever activity you choose. It is advisable to keep a journal when you embark on your long journey of making a science fair project.

It will make it easier for you to keep track of ideas that you have and information that you collect if you keep a regular journal. If you have chosen an experiment based science fair project, a journal is invaluable. It will help you record the information from each subsequent experiment with accuracy.

You can then use the data that was generated in the various experiments to make charts and graphs as visual representations of the experiment that you conducted. These visual aids can be used on the display board at the science fair. The journal itself must also be part of the display on the final day.

This will help the judges trace your journey in the science fair project that you will present to them. Naturally there are chances of not keeping up with the journal due to getting side tracked. So you must avoid this. Remember the more organized you are the better the chances of winning that Science Fair medal.