Flexi Says: Some error or uncertainty always exists in any measurement. The amount of uncertainty depends both upon the quality of the measuring tool and upon the skill of the person making the measurement. Scientific tools may come with an uncertainty estimate. For example, a particular model of electronic mass balance may report an uncertainty of 0.25mg when measuring a 100g mass. The person measuring may also make a judgement about the uncertainty value of a tool based on how difficult it is to determine the smallest digit of the measurement. Experimental uncertainties based on skill must be estimated by the person or people conducting the experiment. Typically, this involves taking multiple measurements of the same object or variable and reporting the range of outcomes.