The better proportioned these facets are on the diamond, the more light will be reflected back to the viewer's eye. This is extremely important. When cut properly, the diamond will sparkle more. Diamond cuts are measured by the table percentage, so always ask for it. If you are having a diamond mounted, write down the measurements of your stone.
Measurements never change.
Larger diamonds often cost more per carat due to their size. There are 100 points to a carat. Always get the actual point size of a diamond rather than a fractional weight. Sometimes jewelers will try to sell a .90 diamond as a 1 carat diamond. A .90 diamond should be substantially less expensive.