Avoid the perils of using rounded data.

From a purely technical point of view it is always better to work with recorded/unrounded data. This paper discusses reasons why despite this, rounded data used for reporting may have been used in the past in calculations and visualisation. If rounded data are used then it is recommended that a risk assessment of the impact of the rounding is performed. If it is not possible to use unrounded data (with many decimal places) then the authors recommend that the data used should have at least two decimal places more than the number of decimal places required in the reported value ("effectively unrounded data"). Examples are given to illustrate the importance of using effectively unrounded data in visualisation and numerical calculations. It is recommended that effectively unrounded data and, if required, reported data are listed in reports. The implications of using rounded data when making formal assessments against specification limits is also discussed and guidance is provided on the use of nominal and effective specification limits.