Repeated measurements
The idea
Measurements vary because of instruments, observers, and natural differences. Repeating a measurement helps assess consistency. A mean summarizes values but does not erase variation. Keep unusual results unless you have a documented reason that a measurement is invalid.
Worked example
Flights of 4, 5, and 6 meters have mean distance 5 meters. Their range is 2 meters. Another design with the same mean but much wider variation may be less consistent.
Another application
The sets 4, 5, 6 and 1, 5, 9 both have mean 5. Their ranges are 2 and 8. If consistent performance matters, the mean alone cannot tell you which set is more consistent.
A common misunderstanding
A mean without a description of spread can hide important variation. Record the original measurements rather than only the average.
Try it yourself
Measure the same object five times using a ruler. Record all results, their mean, and their range. Discuss the instrument’s smallest markings.
Check your understanding
What is the mean of 2, 4, and 6?
Reveal the explained answer
4: the sum is 12, divided by three measurements.