If you create charts with Excel, error bars allow you to visualize margins of error for data points. Here's how to add error bars in Excel.

How to Make Box & Whisker Plots in Excel 2007. Microsoft Excel, a spreadsheet and data analysis program, is available as a stand-alone program or as a component of the Microsoft Office ...

Suppose you have some data. You want to plot that data and turn it in with your lab report. Your instructor (me) told you to be sure and include error bars on your graph.