>>> a similar mistake, I suppose, to the Thais calling the ground floor '1st floor'!

I am not sure if we (Thais) have made a mistake or we have been confused. I have an impression that the British use underground, ground floor, 1st floor, 2nd floor and so on; whereas, the Americans do not say ‘ground floor’ but use underground, 1st floor, 2nd floor respectively. Buddha knows how the Aussi, Kiwi, Canadian and Irish say about this.

Welcome corrections if I misunderstand. Thank you.