Clarity: Clarity assesses the internal characteristics of the diamond as it formed in nature. This C factor is graded on a 10-grade scale and also impacts the diamond's rarity and value.
The fastest marathon ever was run by Geoffrey Mutai (2:03:02) at the Boston Marathon on April 18, 2011. But because the legendary Boston course does not meet IAAF layout standards, the World Record belongs to Patrick Makau (2:03:38) recorded at the Berlin Marathon on September 25, 2011.
The Fuzzy Math Problem. Most runners plan for a faster marathon by reverse engineering their desired race day performance into a long run training pace. Someone looking to go from a 3:45 to a 3:30 marathon will do the math to figure that they need to run about an 8 min/mile pace on race day.