SI units, other known as the international system of units is used for finding the length or magnitude of an object. The only unit that is reasonable to measure a rope is a meter because it is longer then the other units and depending on how long the rope is, it's faster to calculate the length of the rope.
Paris, and the meaning behind this is to show that they both honor and respect each other. That their love will kill the pity they feel. Their love will last forever.