Misuse of words is one of the main reasons prevent us from uncovering the similarity between or equality of some concepts in different branches of science and technology which have their own terminology.
The following figures and table have been extracted from:
http://www.nationalaperture.com/slits.htm in which you can find a kind of incorrect use of words.
The word Tolerance in the above table has been used improperly. The correct wording in this case is "Accuracy" or "Precision".
As an example, tolerance or uncertainty of slit width 2.5µm mentioned in the second row of above table is equal to (+1)-(-0.5)=1.5µm. Tolerance is always positive.
Tolerance = Upper Deviation - Lower Deviation