The following videos demonstrate how a simple linear line of best fit (trendline) may be added to an Excel graph.

The first video starts quite simple, demonstrating how to add a trendline to data, and then discusses how to format certain features of the trendline, such as setting a fixed y-intercept, extending the line forwards or backwards anddisplaying an equation for the line on the graph.

The final part of the video is more advanced, dealing with the issue of anomalous data. Anomalies can distort trendlines since Excel has no way of distinguishing anomalous data from reliable data. The second part of the video demonstrates how to exclude anomalies from you main data series and then how to add them back onto the graph as separate points.

Adding Trendlines to Science Graphs in Excel: part 1

The second video demonstrates how the uncertainty in the gradient of a trendline may be calculated. This is a much more advanced proceedure, but is required by some science qualifications such as the International Baccalaureate Diploma Programme. The technique involves adding error bars to you graph and then displaying trend lines of maximum and minimum gradient which pass between these error bars.

Adding Trendlines to Science Graphs in Excel: part 2