The unit of length, metre was originally defined as the distance between two fine lines engraved on gold plugs near the ends of a bar of platinum-iridium alloy that is kept 0^@ C. Then the unit was defined in October 1983 in terms of wavelength of kr. 86 radiation . Now, the present unit is defined in terms of distance travelled by light . In your opinion, which of the two essential requirements for a standard unit availability, invariability played the key role in this modification.

The unit of length, metre was originally defined as the distance betwe

1.	The unit of length, metre was originally defined as the distance between two fine lines engraved on gold plugs near the ends of a bar of platinum-iridium alloy that is kept 0^@ C. Then the unit was defined in October 1983 in terms of wavelength of kr. 86 radiation . Now, the present unit is defined in terms of distance travelled by light . In your opinion, which of the two essential requirements for a standard unit availability, invariability played the key role in this modification.
Answer» SOLUTION :INVARIABILITY.