The geometric modeler works with a set of two tolerances which are
defined as follows: 
Point tolerance

Two objects closer than the point tolerance are considered as equal.
The point tolerance value is 0.001mm. 
Example 1 
It is impossible to create a line between two points whose distance is
less than the point tolerance. 
Example 2 
A curve whose distance from a surface is less than the point tolerance
can be laid down on this surface (to create a parallel curve for instance). 
Angular tolerance

An edge with a sharpness smaller than the angular tolerance is
considered as smooth. The angular tolerance value is 0.5 degree. 
Example 1 
A shell composed of two faces whose angle along their common edge
varies from 0.6 to 1 degree is not considered as smooth. This surface has a
sharp edge which can be made smooth by using the EdgeFillet capability. 
Example 2 
A shell composed of two faces whose angle along their common edge
varies from 0.3 to 0.6 degree is not considered as smooth. 