Platinum-Iridium meter bar
This was the standard of length for the SI (Metric system) from 1889 until 1960, when the SI system changed to a new definition of length based on the wavelength of light emitted by krypton 86.
Unit Information
It is a unit of Length
Symbol m
Unit System SI base unit

metre(or meter) is the fundamental and Standard International unit of length. Since 1983, it has been defined as "the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second".