Take note of trends, observations, and other noteworthy items when you annotate the charts you’ve created with Google spreadsheets. Annotations are text notes that can be attached to either a specific data point on your chart or as a label along your chart’s horizontal axis. They’re currently available for line and area charts only.
How to annotate
Annotate a chart by creating a separate column filled with your annotation text to the right of the data points or horizontal axis you’re annotating.
Enter the annotation text in the column to the right of each data point. If, for example, labels for your horizontal (X) axis are in Column A and corresponding data points for your vertical (Y) axis are in Column B, you’d add your annotations for each data point in Column C.
Enter the annotation text in the column to the right of the data that corresponds with the horizontal axis. If, for example, labels for your horizontal axis are in Column A, add annotations in Column B and put data points plotted against each label in Column C.
Or, customize your chart. Learn how