Here’s an idea to ensure that lineside structures, such as platforms, poles and bridges, are correct relative to the track running edges.
This is an EMGS Manual structure gauge copied onto a piece of 30-thou plastic and stuck onto a scrap wagon with EM wheelsets.
In use, in the second photo, the wagon is proving that the platform edge is at the right distance from the track and that the platform edge is a little low; as this is the loco coal loading point on an industrial line a low platform is not a problem.
It’s sold as “N-gauge ballast”, being single size stone marketed usually by Gaugemaster, among other sources, as I find that the stuff sold for 4mm is too coarse and far too Plasser &Theurer for me.
It’s washed into place with an old paintbrush using woodworking adhesive watered down to the same consistency as milk, and with some washing up liquid added in. Bit messy to do though very therapeutic.