"If you go to the shop to buy boards for building a shelf - do you measure the board by stepping on it?"

I do actually. Or rather, before I got out to buy some something where accurate measurements aren't that important I'm very likely to step it out, or use the width of my hand, which is close on four inches. No point in being more accurate than you need to be.

"...the distances are already given in kilometers in Ireland" Except where there are still old signposts up giving them in miles. I'm pretty sure there are still a fair number of them. For a long time it was confusing because there were signs of roughly the same vintage, some in miles and some in kilometres, and no indication of which.

It's silly name for a unit of measurement anyway - no settled way of spelling it or pronouncing it.

I'm glad the Americans are sticking to the old measurements (even if they do get them wrong from tiem to time - niotably the pint and the gallon). I always find it pleasing the way the USA goes on about being a modern country, when in many ways it's among the most old-fashioned places there are (that is a compliment in my books).