The Origins of the P4 back to back gauge?

[Penrhos1920]

Is this where the back to back gauge originated?

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[Bilton Junction]

It looks more to do with packing the height of the track and checking that the cut ends are square rather than gauge. But it does look a bit small for 308 mm to the foot gauge. It is interesting to see that the rail appears to have been painted, presumably with bitumen in the area covered by the fishplate.
Carl

[Bilton Junction]

But perhaps it is just a gauge to keep the right gap when the next section is hoisted into place. You would still think that that farty little gauge would drop out in the ballast never to be seen again, pretty much like the model version. There is one good thing about P4, complete pain that it is, it does make you look at the way things were done full size!
Carl