Summarize the basic physics of your experiment. Include equations and other principle things the reader would need to know in order to understand the experiment 4. Describe briefly how you carried out the experiment. Do not include relatively trivial things like turning on a switch. On the other hand, you should include descriptions of how you determine things that are necessary to the anticipated results.
Percent error is used when comparing a result to an accepted value.
The average of the two measurement is probably closer to the actual value than either measurement. So, the average is used in the denominator. This section should be a concise, tabulated summary of your results. However, don't always expect to get accuracy this good. The nature of the experiment has a bearing on the expected accuracy.