The cut and carat are measured using machines, but the color and clarity are determined by human eyes aided by magnification loupes. To know that the grading of your newly purchased 3-carat halo diamond ring is accurate, you need to check its diamonds certificate. As long as it is from a reliable gemological institute, it can dependably establish the particulars of the stone. This makes insisting on certified diamonds while buying jewelry online a wise move. Many brick and mortar stores make sure to sell nothing but GIA certified jewelry, and you should make sure to stick to those. The problem with uncertified diamonds is that you cannot be sure of the quality of workmanship they claim to carry, and sometimes, you can even get saddled with inferior stones which simply look like they are worth what you paid for them.