Thats one way, an easier way is to reference both the maps together, both have kilowatts on the left at the same intervals but on the right one is psi the other rpm, so if you have a look at the psi map you will see that full boost of 18psi hits at a tad under 168kw, on the rpm map you go to 168kw follow that line to the right and you will see that full boost is at 6000rpm