TABLE OF CONTENTS If we know that the balance has been correctly calibrated, checked before use and used properly, then there will be no systematic bias away from the true result in the weighings made on it. The average of several weighings of a single stable object, such as a standard mass, will be very close to the true weight, so the balance weighs accurately.
At some level of measurement there may be some variation in repeated weighings but we expect this to be extremely small compared with the weight itself so the balance weighs with good precision as well as good accuracy.
Usually it is not possible to do a number of replicates of each test result in order to determine its uncertainty. However the uncertainty associated with different stages of the test procedure can be determined in advance and an overall combined uncertainty estimated for the test method.
The practical exercise with the pipette shows how the uncertainty due to one component of a test method could be measured. In this case we expect measurements made with both the balance and the thermometer to be both accurate and precise. Most of the uncertainty in the measurement of the volume of repeated pipettings of water would arise from the pipetting technique.
In a test procedure there may be uncertainty due to several volume measurements by pipette or volumetric flask that could affect the final result. In addition...
