Listed in the forthcoming Talisman Auction is an "early GNR tablet" of a type I have never come across before (lot 364 if anybody wants to see it).
It is lettered "Go on to Essendine" on one side, "Go on to Stamford" in the other and, according to the catalogue, designed to be mounted on a bracket in the engine.
It does not look as though it is designed to fit in any type of electric instrument, so would this effectively have been worked as a simple OES Staff?
The two cast iron sides are painted different colours - why should the direction of travel be colour-coded?
Or does the unorthodox "Go on to ... " wording imply that this was not merely a normal authority to occupy a single line ?