I assume thats the octane rating on the nozzle? I like that idea. 91 doesn't seem much for super+ unless their octane system is different to ours. Which wouldn't surprise me.
Definitely different. I've seen a few articles regarding this.
A quick snippet from Google
In Europe, the octane rating on the pump is simply the RON figure. America, by contrast, uses the average of the RON and the MON figures, called the AKI (anti-knock index). Thus, 97 octane “super unleaded” in Britain is roughly equivalent to 91 octane premium in the United States.
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