Accuracy, Precision and Uncertainty in Measurement

Accuracy is about how close your measured value is to the true, actual value of that quantity.

Precision is about getting reproducible results. If you measure the same thing multiple times and get nearly identical answers, your measurements are precise.

In real experiments, it is very difficult to get exactly the same answer every single time. This difference or possibility of error is called uncertainty.

Aim

To determine if the length measurements of a single piece of cloth, taken by multiple observers using the same type of instrument, are identical, and to identify the potential sources of uncertainty that cause any variations.

Procedure (Hypothetical)

1. Gather: Provide ten different students with a piece of cloth and a metre scale.
2. Instruction: Instruct each student to measure the length of the cloth and record the value, aiming for precision up to the millimeter (mm).
3. Data Collection: Collect the ten recorded measurements from all the students.
4. Analysis: Compare the ten recorded lengths to check if they are identical.

Observation

When the ten measurements are compared, it is highly likely that the recorded answers will not be identical. Small differences, possibly in the millimeter range, will be observed among the values.

Result and Reasoning

The measurements are not identical because the experiment is affected by possible uncertainties in an observation.

The source identifies the following reasons for these uncertainties:

• Skill of the person doing the experiment: Each of the ten students possesses a slightly different level of skill when performing the task. This variation in skill will affect how accurately they align the metre scale with the cloth's edge and how precisely they read the final value, leading to different results.
• The method used for measurement: Although all students use a metre scale, slight variations in their measurement technique (like the viewing angle when reading the scale, known as parallax, or how they position the scale's zero mark) can introduce discrepancies.
• Quality of the instrument used: Even if the instruments are all "metre scales," there could be minor variations or imperfections in the individual scales they use. This minute difference in instrument quality can cause slight variations in the final readings recorded by the students.

Accuracy (Checking a phone's GPS): When you use a phone's GPS for navigation, its accuracy is determined by how close the location it displays on the map is to your actual physical location.

Precision (Manufacturing Bolts): A company manufacturing small metal bolts needs high precision. Every bolt produced must have a diameter that is nearly identical to every other bolt, ensuring they all fit the intended nuts perfectly (i.e., reproducible results).

Uncertainty (Taking a Fever Temperature): The temperature reading you get when you measure a fever can have uncertainty due to:

1. Quality of the instrument: A cheap or old thermometer (instrument quality).
2. External or internal factors: Whether you just finished a hot drink before measuring (external/internal factors).