Tips on How To Write a Scientific Figure Legends for a Laboratory Report
A figure legend is a chunk of text that accompanies each figure in a laboratory report. Its purpose is to explain the figure clearly and thoroughly, providing readers with all the information necessary to understand the figure without returning to the main text of the lab report. Publisher guidelines, instructor requirements and style manuals vary to some degree in the content, placement and style they specify for figure legends, however, so it is essential to read the relevant instructions carefully and observe with precision and consistency every detail they provide about preparing figures and their explanatory text.

You will first need to decide whether legends are the correct choice for the figures in your lab report. Some instructions call for captions instead of legends, and some require both legends and captions. If only one of these options is indicated, the figure legend or caption should appear beneath each figure, generally formatted to match the width of the table and use a slightly smaller font than the main text of the lab report. If both caption and legend are required, the caption usually appears beneath the figure while the legend is incorporated into the figure, often enclosed within a box for clarity. When this is the case, figure captions function more like titles and legends more like explanatory notes, which can be a helpful distinction when you are trying to decide which bits of information to include in each, but it will not apply universally, so careful attention to guidelines and the examples they offer is always necessary.

Assuming that only figure legends are required, which is certainly the case for many lab reports, each legend should act as an explanatory summary of the figure. The opening sentence might be a concise description of the experiment or other research method or it could be a statement about the results or evidence obtained. Methodology is usually explained briefly but comprehensively, providing enough detail for readers to understand what the figure presents and perhaps enough for researchers to repeat your work. How much detail should be offered about experimental conditions, methods and results will depend on whether your lab report has separate sections of text dedicated to methods and results or lacks these sections and uses figures and other visual tools for conveying the information. Accuracy and precision are always required, however, as are the details necessary to understand the figure on its own, so research subjects and sample sizes, confidence limits and probability values, symbols and patterns, nonstandard abbreviations and measures, specialised terminology and indeed any elements that may be potentially confusing for readers should be defined or explained in the figure legend. Finally, if aspects of the figure have been borrowed from elsewhere, appropriate acknowledgements or credits should also be included in the figure legend.

Unless the guidelines or examples you are using indicate otherwise, a figure legend should be written in complete sentences, but most figure legends do not extend beyond 300 words, so the language should also be as concise as possible. The opening sentence might therefore be a descriptive phrase that acts as a title rather than a full sentence, and definitions can often simply be listed with the individual items separated by semicolons. Clearly conveying the necessary information to your readers should be your priority, so it is essential to achieve consistency as well as accuracy and precision when you are constructing your figure legends. The units, symbols, abbreviations, terminology and other elements explained in a figure legend should obviously match those used in the figure itself exactly or your figure legend will confuse matters instead of clarifying them. These aspects should also remain consistent across other figures in your report and in your discussions of methods and results in the main text of the document. Such consistency will not only enhance reader comprehension and thus the successful communication of your research, but also give your lab report a tidy and professional appearance.