People in the trade often estimate a diamond’s table percentage. Estimation techniques require less time and less equipment and, with practice, can be accurate within one or two percent. Estimation techniques are most reliable with diamonds that have table percentages between 50 and 70 percent.
There are three estimation methods: ratio, bowing, and flash.
With the ratio method, you compare two sections of a diamond-from the girdle edge to the edge of the table, and from the edge of the table to the culet-and determine the ratio between them. Certain ratios are fairly common and have approximate corresponding table percentages.
Courtesy: GIA. Resource: Amanda. #eClarity