If you write «in-character standardised measurement» I am going to agree. Authentic in-character measurement is very rarely going to be standardised or as accurate as we are used to. And in this view there is no conflict between modern use and period use. The point is, sloppy measures work better narratively. And we who are brought up to think in metres, will treat a foot in the same way. It is the length of somebody's foot.
But you are absolutely right that this should be made clear in the core rules. And consistently treated. I have a feeling that some authors have been thinking in terms of accurate measures (ten rounds to a minute and a pace is a yards) and some in terms of narrative sloppiness (6-10 rounds to a minute and a pace is the length of a step).
Of course, if the players read the rules with the same sloppiness, it does not matter, but it only takes one engineering nerd to create tension in the troupe.