Repeated tests for reliability
Distinguish between precision (consistency of repeated readings) and accuracy (closeness to true value), use significant figures and standard form correctly, and choose and use appropriate measuring instruments to minimise uncertainty
What a learner can do afterwards
- Explains the distinction between precision and accuracy with examples
- Rounds measurements to an appropriate number of significant figures
- Selects a measuring instrument with appropriate resolution for the context (e.g. choosing a 10 ml measuring cylinder rather than a 1-litre measuring jug for a 5 ml measurement)
The lesson
When you measure something several times, two different questions matter. Do your readings agree with each other? And do they match the true value? The first question is about precision. The second is about accuracy.
Priya measures a pencil three times with a ruler and gets 15.2 cm, 15.2 cm, and 15.3 cm. Her readings agree closely, so they are precise. If the pencil's real length is about 15.2 cm, she is also accurate. But if her ruler had a bent end and the real length was 14.0 cm, her readings would still be precise. They would just be precise and wrong.
Pick an instrument that matches the size of what you are measuring. A 10 ml cylinder lets you read a 5 ml sample far more precisely than a 1 litre jug would. When you write down a result, only use as many significant figures as your instrument can actually support. Extra digits don't make a measurement more true.
Precision means repeats agree with each other, accuracy means they agree with the true value, and more repeats alone can't fix a badly calibrated instrument.
Watch it
Where it sits
Learn first
This opens up
Where this leads
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.