Reference the source where you have taken the diagram from. For example, if you found it in a book, reference the book; if found on a website, reference the website etc.
You should provide an in-text citation for any diagram that you reproduce in your work. The citation would normally be given after the caption/title of the diagram. Include the page number(s) if coming from a printed source.
Figure 1. Flowchart for estimating of the sizing parameters based on MLP (Mellit et al. 2009, p.411).
Follow the format for the source you have taken the chart, table, diagram or graph from. Use the relevant example from this guide to identify the format your reference should follow.
You may want to include the page number or number range indicating where you found the information you are referring to for some sources. For guidance on how to do this see the ‘Page numbers for in-text references’ section.