It's important to check the results from an experiment. Does the result make sense? Does it follow from other facts that are known? From the standpoint of teaching High School science, checking if one's results are sensible adds an additional layer of safety that the results are correct. (From the standpoint of advancements in Science, a basic research tenet is that results must be repeatable and not just a fluke.

The length of the day is something we take for granted. Yet, much can be learned about the day -- and the way the Earth moves -- from careful observations of the Sun and a more distant star, over as little as 24 hours, with a home-made viewer and a good clock.