At the recent Uckfield Model Railway Exhibition, a member of the public tried to suggest that quoting the track gauge to a thousandth of an inch was a bit extreme, and why not use 0.9” instead? Well, ignoring the trite response that 0.9” can also be expressed as 0.900” – and often is in engineering circles to specify the required level of accuracy (which otherwise covers 0.850” to 0.949”), the simple fact is that we don’t actually use the decimal fraction, merely divide 56 ½ inches (standard gauge) by 64, and then express that result in a decimal format… (And yes, I know that results in 0.883”, and the SSMRS standard is 0.884”, but there are technical reasons for that, due to engineering tolerances required for an exact scale wheel profile.) In truth, when I started in S, I didn’t have a track gauge, but I did have a (cheap) vernier calibre which was calibrated in 1/128” of an inch – scale half inches in S scale: I quickly took it to ⅞” (a scale 56 inches, and used the fine adjustment to add the extra single graduation – an extra 1/128”, or 0.008” if you must have it as a decimal!)

I recently realised that when we say S scale is 3/16” to the foot, this is slightly misleading. It is entirely true, but it happens to the result of simplifying 12/64”, which latter possibly expresses the vulgar fraction in a way that explains exactly what we are doing by referencing the scale ratio. But we run up against people thinking we measure everything in terms of how many 1/64” it is (like 120/64” for a scale 10’) which is patently silly but reflects the poor standard of mathematical understanding in everyday life. For the record, when using mental arithmetic it gets much quicker, as ¾” represents 4’ on the prototype, 3” 16 feet and so forth. Or one can buy a “scale ruler” and just that! (Ten feet is 1 ½” – a scale 8’ – plus ⅜” – a a scale 2’ – which results in 1 ⅞”, or ⅛” less than 2”.)

And whilst we are about it, the MRSG and the P4 society invented neither “true scale” model railway standards nor indeed “finescale railway modelling”: they merely promoted it in the most popular scale in the British Isles. Aside from the rarely acknowledged systematic derivation of the track standards for S scale undertaken by Ian Pusey in the early 1960s (which influenced the self-styled “Model Railway Study Group” soon afterwards) people like Jim Richards, working in 7mm scale, had been dividing prototype dimensions by their chosen scale ratio for years beforehand, and Charles Wynne effectively defined finescale back in 1919, when he set himself a standard of accuracy for his own modelling (to the nearest scale inch: maybe not much compared to some, but a lot better than what was going on elsewhere at the time!) The same is true about the benefits of allowing wheels to move up and down, whether sprung, “compensated” or via a mixture of the two, as the prototype often did.