Oh dear, Kurfurst has gone on another one of his rants.
The Merlin in Perspective, no.2 in the R-R Heritage Trust's Historical Series
"
Before the end of the Battle Spitfire IIs with Merlin XIIs were in service, with the supercharger gear ratio increased from 8.58 to 9.09:1 giving a better full throttle height
at 12lb boost......"