Writing Guide Home Uncertainties  

Uncertainties are used to reflect the range of possible error when measuring and you should always try to quantify it.

They are always shown as a ± after the SI unit of a measurement.

Uncertainty can be shown for the following (not an exhaustive list)

• Equipment
• Calculated data such as speed where you would use length and time you measured
• Biological uncertainties
• Chemical uncertainties

The level of precision for a piece of equipment would indicate the uncertainty. If a measuring cylinder has a graduation every 10 cm3 then the level of uncertainty would be ± 10 cm3.

You can also have an uncertainty based on human reaction times which you would have to work out for yourself. You have to explain how you estimate such an uncertainty. Biological uncertainties should show the level of uncertainty cause by an organisms. You minimise biological uncertainties by using a large sample, same species and from the same source. If you are investigating osmosis using potatoes, you would try and use pieces of potato from the same potato rather than from different ones let alone from a different variety of potatoes.

Chemical uncertainties also play an important role. It is worth considering if the chemicals have all come from the same batch as different batches may have slight differences which could affect the outcome.

Whenever you show data, you should indicate the level of uncertainty.