Diamond grading is subjective. The location of inclusions can mean that not all diamonds with the same grade are the same. The same quantity and size of inclusions on 2 diamonds with the same VS grade can look drastically different because of their location, and their orientation to the desired setting.
The 4 C’s of Diamond Buying according to the GIA: carat, cut, color and clarity.
A diamonds size is measured in Carat Weight. Each diamond carat is also equal to 100 points. For example, a diamond that is a ½ carat can also be referred to as a 50 point diamond.
The cut of the diamond is also referred to as the shape. Shapes include Round Brilliant, Princess Cut, Emerald Cut, Marquise Cut, Oval Cut, Radiant Cut, Pear Shape, Hear shaped and Assher Cut. When a diamond is cut to good proportions, light is refracted from one facet to another, then dispersed through the top of the diamond. A well cut diamond - regardless of its shape - sparkles, has more fire and offers the greatest brilliance.
Color is the natural body color visible in a diamond and is the one C determined completely by nature, not man. As a rule, the closer a diamond is to colorless, the more valuable and beautiful it is. Diamond colors appear in a range from D to Z. Color grades D, E and F are considered colorless, making them rare grades G, H and I are near colorless; and grades J down are going to have a considerable amount of color.
Clarity is an indication of a diamond's purity. When a rough stone is extracted from carbon, deep beneath the earth, tiny traces of natural elements are almost always trapped inside. These elements are called inclusions, though sometimes they are referred to as birthmarks, because they are formed naturally and are unique to each stone. Clarity ranges from flawless (FL); internally flawless (IF) very very slightly included (VVS1-VVS2) very slightly included (VS1-VS2) slightly included (SI1-SI3) and included (I1-I3).