how is linear metre calculated?

Answer 1

It has had many definitins, starting off with 10,000,000 part of the distance from NorthPole to the Equator calculated by the French.

Then, it was the distance on a bar on metal held in Paris.

Now it's measured as the distance travelled by light in vacuum in 1/299,792,458 of a second!

PS Tat - Well spotted!

Answer 2

Markymark lost a zero somewhere. It is "1/10,000,000 of the distance from the equator to the north pole through Paris". More precisely, it is along the earth's surface (arc), i.e. not the straight line through the earth.

Also note that Oct 20,1983 the meter was redefined to be 1/299,... with the time unit of "second" determined by 1 part in 10 to 14th uncertainty of a Cesium clock. At similar accuracy the iodine stabilized Helium-Neon laser ...radiation for realizing the meter ...wavelength...is 632.99139822 nm.

The English measurements of inches and feet are actually redefined using SI metric measures with 1 inch equal to exactly 2.54 cm.

Answer 3

It is defined by wave lengths of light from a constant source. Historically, the metre was defined by the French Academy of Sciences as 1/10,000,000 of the distance from the equator to the north pole through Paris.