An eccentric tube is one which has the centre of the circle formed by the OD (outside diameter) which is at a different point from the centre of the circle formed by the ID (inside diameter), so the two circles are not concentric. Eccentricity can be checked by determining the wall thickness around the tube at any cross section to establish maximum and minimum.
The tube’s eccentricity (in mm) at that cross section would be one half the difference between the minimum wall thickness (t2) and the maximum wall thickness (t1).
