Literal Translation
To be next to the plaque/turntable
Actual Meaning
To miss the point, way off the mark, be clueless
Etymology
We are entering the realm of railways… The ‘plate’ in question is the turntable that can move a locomotive from one track to another. In some marshalling yards, the turntable or swing bridge is located in the ‘roundhouse’. Once the engine is on the turntable, it rotates to face the chosen track, often allowing the train to return to the depot. A wrong manoeuvre can cause the locomotive to slide into the pit usually located under the turntable, or roll between the rails. In this case, it was said that the locomotive was ‘off the turntable’, an expression that has become widespread for any situation where thigns go off the rails!