When discussing the manufacture of a part DO NOT say it has to “very accurate” or “exact”.  There is no such dimension as 10mm, a part is manufactured to 10mm plus or minus a certain tolerance that is its accuracy.

As well as considering simple dimensional tolerance of a feature, say plus or minus 0.01mm on a length or diameter, we also have to consider the Geometric Tolerance of a feature – how flat or how round something is, what the envelope of deviation is – Wiki discussion

Making something to a high tolerance is not necessarily a good thing,high tolerances cost time and money, artifacts should be made to an appropriate tolerance – we would not build a shed to the same tolerance as we would manufacture a mechanical wrist watch!

The main reasons for being aware of accuracy in the virtual CAD model are regeneration times and interaction between parts with differing accuracies. The real world impact of accuracy setting would only come into play if you worked with, for example, very large parts or very high accuracy (aerospace) parts.

Creo provides two methods to define accuracy: relative and absolute – the default is relative accuracy.

 

Relative Accuracy

The part accuracy is relative to the greatest dimension of the part. The default setting is 0.001, therefore the accuracy of our 2m by 1m shed would be 2mm and a 3mm part in our watch would be .003mm

But what if you have a 10mm cube part which has a long thin tube protruding from the side?  If the tube was 1m long your Relative accuracy would be 1mm – not good for the 10mm lump on the end.  This may be a situation where you switch to;

 

Absolute Accuracy

An absolute figure which all features are calculated to.  In the above scenario we may switch to an Absolute accuracy of .01mm

Another factor to consider if your thinking of making large components to a high accuracy is Thermal Expansion – a 1m length of aluminium will increase its length by 0.23mm if its temperature is raised 10 degrees.  Environmental conditions need to be considered with reference to tolerancing scheme.

 

Setting Accuracy

Be aware assemblies have an accuracy setting as well as part files.

File > Prepare > Model Properties > Materials > Accuracy > Change

Warning: models and assemblies will need to be regenerated after changing accuracy and features – particularly those with (relatively) small elements – may fail.