We’ve created a new video that explains the definition of the primary normal for length and how coordinate measurements can be traced back to it.
The primary standard is the ultra-precise reference to which all length measurement instrument calibrations must be traceable.
In Denmark, the DFM is responsible for the primary standard for length. In the past, the primary standard was a very precise platinum rod of a 1-meter length, but today light is used to define the primary standard.