definitions and concepts

• accuracy

  a measure of how close a measurement is to the true value
• precision

  a measure of how close a measurement is to the mean value

  • only gives an indication of the magnitude of random errors, not how close data is to the true value
• random error

  unpredictable variation between measurements that leads to a spread of values about the true value

  • random error can be reduced by taking repeat measurements
• systematic error

  causes all readings to differ from the true value by a fixed amount

  • repeat readings cannot correct systematic error, instead a different technique or apparatus should be used
• repeatable

  the same experimenter can repeat a measurement using the same method and equipment and obtain the same value
• reproducible

  an experiment can be repeated by a different experimenter using a different method and different apparatus, and still obtain the same results
• resolution

  the smallest change in a quantity that causes a visible change in the reading that a measuring instrument records
• uncertainty

  the interval that a value is said to lie within, with a given level of confidence