THE METER
 

The fundamental unit of distance, length, linear dimension, or displacement (all different terms meaning essentially the same thing) is the meter, symbolized by the lowercase nonitalicized English letter m. Originally, the meter was designated as the distance between two scratches on a platinum bar put on display in Paris, France. The original idea was that there ought to be 10 million (10⁷) meters along a great circle between the north pole and the equator of Earth, as it would be measured if the route passed through Paris (Fig. 1). Mountains, bodies of water, and other barriers were ignored; the Earth was imagined to be a perfectly round, smooth ball. The circumference of the Earth is about 40 million (4.0 x 10⁷) m, give or take a little depending on which great circle around the globe you choose.
Nowadays, the meter is defined more precisely as the distance a beam of light travels through a perfect vacuum in 3.33564095 billionths of a second, that is, 3.33564095 x 10^-9 second. This is approximately the length of an adult’s full stride when walking at a brisk pace.

Fig. 1. There are about 10 million meters between the Earth’s north pole and the equator.