Ruby

Ruby is the name given to the red variety of corundum. Ruby is sapphire's sister stone and is second only to diamond in hardness.

Ratio

Ratio refers to the length-to-width relationship of the diamond and is determined by dividing the length measurement by the width measurement. The string of numbers relating to the measurement of a diamond are indicative of its length, width and depth. For instance, if a diamond's measurements are 6.09 x 4.35 x 2.67, then 6.09 is the length in mm, 4.35 is the width and 2.67 is the depth. In this case the ratio would be 6.09 / 4.35 = 1.4. Read more about which ratios are best for different shapes.