Length

Length The meter (m) is the SI unit of length. Historically, this length was defined as one ten-millionth of the distance between the equator and the North Pole along the meridian through Paris . This distance proved to be difficult to measure accurately. So in 1889, the distance between two scratches on a bar made of platinum-iridium alloy held at a specified temperature was adopted as the new standard. In time, the precision of this standard also proved inadequate and other standards were created for the meter. Currently, the meter is determined using the speed of light through empty space, which is defined to be exactly The meter, then, is the distance light travels through empty space in second. By using these definitions, the units of time and length are accessible to laboratories throughout the world.