Peter Butler wrote: Tue Jul 03, 2018 10:41 pm
My guess is that they indicate a position where there is a change in gradient on the track....
Yes, that's it. There's more detail here:
http://www.railsigns.uk/sect24page1/sect24page1.html, but in brief:
"Gradient posts are placed, facing the track, at each location where the gradient of the trackbed changes. Most gradient posts comprise a pair of arms, one on either side of a post. The arms are inclined up or down to indicate the direction of the slope and each one has the value of the relevant gradient marked on it. Gradients are expressed as a ratio, e.g. "1 in 200" (or "1:200"). For example, "1 in 500" means that the track rises (or drops) one unit for every 500 units travelled horizontally. Note that a smaller number in the second part of the ratio indicates a steeper gradient. Some patterns of gradient post omit the first part of the ratio, the value of 1 being implicit.
I don't know that they were terribly common on the narrow gauge, but I could well be wrong there. If you haven't got any gradients you could always use the signs to add atmosphere by propping them outside a hut or shed - here's some speed restriction signs which seem to have lived outside Dunster goods shed on the WSR for years (I think there used to be a 100mph one!), and - coincidentally - a gradient marker showing that the grade changes from 1:223 to 1:143...
Cheers,
Andrew.
It's the accumulation of these small elements that gives our railways their character.
