So, in your book, does,"_WRONG_" mean, "RIGHT"?
"HO", or, "Half O", at the larger ratio, produces smaller models. HO = 3.5mm/foot; OO = 4 mm/foot.
The continentals were using HO, giving a track gauge of 16.5 mm, which was used by Hornby.
It proved difficult to manufacture British outline models in HO with the electric motors available at the time, and so they were manufactured to the slightly larger OO scale. (Giving the OO & HO description used by Hornby).
The track gauge for OO comes out at 18.83mm, and there are a number of loonies trading under the banner of EM, "Exact measurement" and P4, "Prototypical
4mm" who claim even more accurate models. "Loonies"? Because their oh-so accurate models are usually sadly lacking in other areas that they choose to turn a blind eye to; usually signals.(Cross-posted to produce even more accurate info from EM/P4 loonies)