 |
|||||||||||||||||||||
|
|||||||||||||||||||||
|
Since all experimental measurements have uncertainties, we need to know how much we can trust the measurements. Let's illustrate the idea by considering the mass of an object measured on two different balances. Let's assume that the two balances are accurately calibrated. One measurement is taken on a "crude" balance, and the other is taken on a "sophisticated" balance. The table below shows us how to interpret the two masses.
On a crude balance, we
are able to measure to 1 decimal place. On a sophisticated balance, we are
able to measure to 4 decimal places. The digits that have no uncertainty are
the digits in blue. In other words, the digits
that are in blue are the digits that are CERTAIN.
The last digit of a measurement that is shown in red
always carry an uncertainty due to estimation. 
In scientific work, we must always be careful to write down the quantity of measurements properly and to report and calculate quantities that reflect on the accuracy of the measurements. For these reasons, it is important to indicate the margin of error in a measurement by clearly indicating the number of significant figures. We can determine the number of significant figures for any measurement.
# of sig fig = # of digits that are CERTAIN + 1 final uncertain digit Points to note:
|
||||||||||||||||||||
 All contents copyrighted © 1996-2006 British Columbia Institute of Technology Chemistry Department - 3700 Willingdon Avenue Burnaby, B.C. Canada V5G 3H2 |