Footnotes should be written as narrative, in paragraph form, using standard punctuation. A picture is worth a thousand words. Often the most concise and precise way to present data is to plot it. The challenge is knowing what to plot on which axis. An understanding of the theory behind the experiment should provide clues so that the author can determine how to design a plot.
Some general rules apply regardless of the content of the report.
The figure, graph or plot should have an appropriate title. Restating the axis labels is not an appropriate title. All axes should be labeled with the parameter being plotted and the units of that parameter. The number of values on the axis and the number of tic marks should be sufficient to make it easy for the reader to identify the x and y values of each data point. For example, the concentration of reactants changes because time has passed.