As the original post has gone somewhat off topic, will provide an update.
Today, as I was about to The Dublin Swift at Holyhead, decided opportune moment
to change my speedo to "kmh".
I had practiced at home a couple of times, and it was done very easily in the Settings Menu.
Today, annoyingly when I needed it, that setting was greyed out; I was stationary at the time, waiting to drive onto the ship; the temperature setting could be changed from "f" to "c".
I wondered if it was because I had a route running to my Irish destination; cancelled
route.
Went back to settings; still
greyed out 
On 3rd attempt the speed setting was, at last, not greyed out; don't have my
Owner's Manual with me, but I don't recall any preconditions to my proposed action, apart from being stationary.
Any clues/ anyone had same?
