Beginners in the field often ignore some simple facts concerning the number of significant digits of a result. The use of pocket calculators usually results in values with too many decimal places, regardless of whether this is meaningful. In general, one should use only as many decimal places as are compatible with the precision of your experiments. It may therefore be necessary to determine the precision of a measurement by repeating it several times and calculating the standard deviation.
12.3075 12.3351 11.9949 12.2722 12.3117 12.0766The four decimal places used to denote the results are meaningless, since the repeated measurements indicate that at most the first decimal place is valid (a closer analysis shows that the average of the result is 12.21, with a standard deviation of 0.14).
In addition to the signal variation the accuracy of measurements may become even worse for quantities which are determined by the calculation of differences or ratios.
R = (8.97-8.71)/0.015 = 17.33 Ohm.
If we consider the measuring uncertainty, the calculated resistor may take the following extreme values:
Rmax = (8.98-8.70)/0.014 = 20 Ohm
Rmin = (8.96-8.72)/0.016 = 15 Ohm
Thus the resistance is known with low precision - the accuray is around +/- 15%. Thus the resistance should be rounded to the nearest integer number, decimal places are meaningless and superfluous.