All diamond earrings are measured by carat weight. Normally, people want the biggest engagement ring they can get. But technically, bigger sized engagement ring usually suffer in quality, such as a loss in brilliance.
First the diamond fashion are weighed in a vacuum. Next the colour is determined. The clarity is then estimated only after the engagement ring have been magnified by 10 times.
Because fancy shaped GIA Certified Diamond are not symmetrical like round engagement ring, a broader range of parameters are needed in regards to proportion.