Precision

If we measure results in an experiment, one of the things we need to consider is how precise our measurements are.

Precision is how close multiple measurements are to each other.

For example, if we measure the length of a table three times and get 2.00m, 2.01m, and 1.99m, those measurements are very precise because they are all very close to each other.

However, if we measure the same table three times and get 2.00m, 2.50m, and 1.50m, those measurements are not very precise because they are all over the place.

Significant figures

Sometimes we can write the precision of a measurement using significant figures. essentially, we look at all our non-anomalous results, and we see what the most precise number is that all our results will round to.

If we have these results from measuring the time taken for a reaction to occur:

• 12.38s
• 12.36s
• 12.35s

Then we can round the results:

• All of the round to 10s
• All of them round to 12s
• All of them round to 12.4s
• However, their fourth significant figure is different (8, 6, and 5) so we can’t round any further.
• Our results are precise to three significant figures.

Uncertainty

Another way we can measure precision is using uncertainty: see here.