• Reporting measurements with uncertainty

In the previous two sections, we determined what an error was and how important it is to find the errors in your experimental values.  Now you should ask the question: "How do I report an error?"

The correct way to report a measured value is to give the best estimate of the quantity and the uncertainty, as shown:   

For example, recall the pen we measured in the first section.  We estimated that the pen was 18.2 cm long.  We are also confident we can measure the pen to within a millimeter.  That is, we know the pen is within the range 18.1 cm to 18.3 cm.  Thus we would report that our pen is

18.2 +/- 0.1 cm

Another way to show the uncertainty in a measured value is to use error bars on a graph.  An error bar is a line, drawn on a graph, which shows all the values in the range we have determined is our uncertainty, as shown below:

Now that we have examined how to report errors, let's begin learning how to determine what errors you want to report.  First, we need to classify them, as we will discuss on the next page.