Diamonds have internal flaws, called Inclusions, and surface irregularities, called Blemishes.  Together, they are called Clarity characteristics.  A Diamond's Clarity is based on the relative absence of flaws. The clarity of a diamond is measured with 10x magnification.  When buying a Diamond, the last thing you want is obvious flaws easily seen with the unaided eye.  A Diamond is purchased for it's beauty and radiance.  The more obvious the flaws, the less magical the Diamond.  The best Clarity value in a diamond is an "SI1-2" with flaws in the Pavilion or under the Girdle.  These flaws can be hidden easily with the style of setting you choose.  Once mounted, these diamonds can look flawless to the unaided eye, without breaking the bank.