I have a roller track gauge which I picked up from a bits box at a recent show. The bag it was in said "EM?" and it looked to be about right. However, on measuring it and checking it against my EMGS gauges, it's in fact P4 - 18.83 + 0.65mm checkrails.
Before I put it on eBay, anyone here got an EM one they want to swap for it? Reply off-list, first come first served.
Tony Clarke