Table off-center, abbreviated as T/oc, is the deviation of the table from the central position on the crown when observed faceup.
Technically, in a round brilliant-cut diamond, the center points of the table facet and the girdle plane should intersect the imaginary vertical central line running from the crown through the pavilion.
For both diamond graders and customers, a more practical method to evaluate the deviation of the table facet is comparing the lengths of the bezel facets. Each of the eight bezels has one point that connects to a table point, while the opposite contacts the boundary of the girdle plane. Suppose both the table and the girdle outline are regular. In that case, the lengths (the horizontal distance between the two aforementioned points) of all eight bezel facets should be equal to ensure the table is centered.
A centered table represents or contributes to a balanced arrangement of diamond facets for a higher symmetry grade and more appealing light performance.
If the table is off-center on a round brilliant, not all of the eight measurements are almost identical. For example, Measurement 1 and Measurement 2 do not have equal values in Figure 1 below.
Since proportions and angles correlate with each other in a diamond's symmetry, there are some other symmetry variations related to the table off-center. These include crown angle variation (CV), crown height variation (CHV), misshapen bezel (MB) and so on.
In Figure 2, the diamond has crown angle variation. The left crown angle appears steeper than the right crown angle, making the table deviate toward the left side.
Table off-center deviation is not easy to spot on small diamonds with naked eye. However, as table is typically the largest facet on modern diamonds, table off-center may become pronounced on large stones. Sometimes, it could be spotted without magnification, inducing a first sense of "imperfection" in overall balance.
When shopping online, a high-resolution image of the faceup appearance of the diamond can assist in the inspection. However, in the real world, a minute or minor deviation is acceptable and not bound to be defined as off-center.
We should also factor into other deviation issues in diamonds because the symmetry grade is the result of an overall consideration and is merely part of the final cut grade.