[quote name='Grahame HHC' date='31 Oct 2007, 02:02' post='38283']
Yep, you're right that scale and gauge aren't interchangeable but as the 'N' in 'N gauge' stands for 'nine mm' it means that 'N gauge' is okay as a stand alone description and that "N gauge is 9mm" is really tautology. Plus it's commonly acceptable to add the scale/ratio before or after 'N gauge' to help confirm both the gauge and the scale and thus the country; as in 'the scale/ratio in Japanese N gauge is 1:150'. Strangely in America they say/use 'N scale' which is more incorrect as 9mm is not the scale.
N gauge really does stand alone I agree.
Its amazing how diverse this whole thing really is.... and how most of the significant abberations came from UK modelling! I often have a smile at the comments re model accuracy given the "way off scale" nature of track gauges for UK N, UK OO and UK O scales. (not to mention the atrocuiosly big wheel flanges in N and EU HO Scale)
As to the "interchangeability" of terms...
HO Scale is accurate terminology as both the gauge / scale are correct in ratio - 16.5mm gauge and 1:87 both translate to the same scale/ratio
N Scale is to me an accurate terminology but only for EU "N" and US "N", as in both cases gauge and scale translate near as dammit to 1:160th of the prototype correctly
as to the others, N Gauge alone is as you mention simple 9mm designation, as is HO gauge, but OO and O are not as there are variants.... 2mm scale is an accurate description of both the modelling scale and gauge.
For UK and japanese "N", an accurate description would indeed be a combination of N + the actual scale. Its even more of an issue with the larger scales... Internationally OO means 19mm track in USA and 16.5 in the rest of the world.... and O scale is a no-no as its both "tinplate" and 1/4" to the foot in USA and generally 7mm elsewhere - and yet again track gauges vary - with I think 4+ options between 1/4" & 7mm scales....
I am aware of the arguments but still... I do wonder WHY 19mm was never adopted for OO - Valve gear and the need for better wheel profiles would have been a much harder task for Mfrs but it would have made a HUGE difference to the consistency of the UK modelling scene, which is now fragmented between 16.5, EM and P4. Amusing to0 to think that if this had happened - for the purists - going to P4 would have actually meant it was easier to build a loco!!