Rounding Errors Rounding a number involves the discarding of information, in the form of digits. Sometimes this is acceptable and even desirable, at other times rounding may introduce errors. Whether, and by how much, you should round depends on the number of significant figures that you wish to work with. Thus, if you record two observations as 11 and 11.0 you are implying that they were recorded at different levels of precision. Note that decimal places and significant figures are not equivalent.
Decimal places is the number of digits following the decimal point.
Significant figures is the number of digits excluding leading and trailing zeros. If you round off numbers too early in a series of calculations you can introduce errors. When you inspect your data, prior to more formal analyses, you may find that one or more values is far from the majority of observations. These unusual observations are called outliers . There does not appear to be a universally agreed definition of the term 'outlier'.