bECAUSE THE GRAVITATIONAL CONSTANT ONLY APPLIES (damn capslock) to this region of space under theimmediate mass of this planet. And even onthis planet it varieswith altitude, and some local anomalies here and there.

There is a standard meter.

"1960
        

On October 14, the Eleventh General Conference on Weights and Measures redefined the International Standard of Length as 1,650,763.73 vacuum wavelengths of light resulting from unperturbed atomic energy level transition 2p10 ­ 5d5 of the krypton isotope having an atomic weight of 86. The wavelength is

λ = 1 m / 1,650,763.73 = 0.605,780,211 µm

At different times some national laboratories used light sources other than krypton 86 as length standards. Mercury 198 and cadmium 114 were among these and they were accepted by the General Conference as secondary length standards.

1964
        

Helium-Neon stabilized laser wavelengths were coming into use as length standards. Although the laser wavelength was generally accepted as a secondary standard, its widening use was mainly based on its remarkable coherence. Long distances could be measured by laser interferometry that would be impossible with atomic light sources. Line scales of length are measured by dynamic (fringe counting) laser interferometry at NIST.

1980
        

The iodine stabilized Helium-Neon laser wavelength was accepted as a length standard. It had a wavelength uncertainty of 1 part in 1010 at the time.

1983
        

On October 20, the meter was redefined again. The definition states that the meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second. The speed of light is

c = 299,792,458 m/s

The second is determined to an uncertainty, U = 1 part in 1014 by the Cesium clock. The General Conference made the iodine stabilized Helium-Neon laser a recommended radiation for realizing the meter at this time. The wavelength of this laser is

λHeNe = 632.99139822 nm

with an estimated relative standard uncertainty (U) of ± 2.5 x 10−11.

In all of these changes in definition, the goal was not only to improve the precision of the definition, but also to change its actual length as little as possible." (From Here).