Andy, I think 112 would be correct, if it's measured MON.
MON is octane rated as Motor Octane Number.
RON is measured as Research Octane Number (ususlly rated higher)
PON is the combination divided by 2 (R+M/2) and is what you see at the gas pump.
The highest rating a fuel can have is 120.3.The highest octane fuels burn slower therefore they will not detonate at compression rations of 18 to 1.
Dave