I'm with yotty on this. Fathoms. The original decimal system.
100 Fathoms = 1 cable. 10 Cables = 1 Nautical mile.
So, speed in knots, height in fathoms, vis in cables.
"XXX, you are cleared to descend to 300 fathoms, radar heading North North East by East, report established ILS for runway North West By North Port, RVR 1 cable."
What could be simpler?