Earth's circumference mile in the seventeenth century and the metre in the eighteenth. Earth's polar circumference is almost exactly 40,000 km because the metre was originally calibrated on this measurement (1/10-millionth of the distance between the poles and the equator), which is almost exactly 21,600 nautical miles (being defined as one minute of a degree – i.e. 360 multiplied by 60). It has been described as "the single most important measurement" of the Earth, assuming the Earth to be a sphere (the Earth is an technically an ellipsoid, albeit with just 0.3% flattening). Earth's circumference lines are the foundation of the coordinate
Obsolete Russian units of measurement Peter the Great replace it with the Hindu-Arabic numeral system. The basic unit is the Russian cubit, called the "arshin", which has been in use since the 16th century. It was standardized by Peter the Great in the 18th century to measure exactly twenty-eight English inches (). Thus, 80 vershoks = 20 piads = 5 arshins = 140 English inches (). A "piad" (, “palm”, “five”) or "chetvert" (, “quarter”) is a hand span, the distance between ends of the spread thumb and index finger. Alternative units: As in many ancient systems of measurement the Russian distinguishes between dry and