Metric measurements

It is nature that has given light a velocity and it is man who has given the unit of velocity and time , which is as per his yardstick. The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole . In 1799, it was redefined in terms of a prototype metre bar (the actual bar used was changed in 1889). In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition was adopted.

In the International System of Units (SI), the basic unit of length is the metre and is now defined in terms of the speed of light. A meter has been officially defined to be the distance traveled by light in a vacuum in 1/299,792,458 second. All other length and distance measurements in the metric system derive from the meter (eg. km= 1000m, 1m= 1000mm). The centimetre and the kilometre , derived from the metre, are also commonly used units.

Conversion

The process of changing from one type of system to another. The process of conversion depends on the specific situation and the intended purpose. This may be governed by regulation, contract, technical specifications or other published standards . A conversion factor is used to change the units of a measured quantity without changing its value.