I believe there is a pressure sensor on the pump/rail. If they are wildly changing pressure,(and it does from 750-2200psi) then they are going to need to know exctly what that pressure is to calculate what injector flow will be at that instant.

had to work late tonight, prolly get started when I get home. As a side note I stayed up late last night building a mold from the stock engine cover. MMM red/black carbon fiber.....

MY wife wants turbo anodized PURPLE! when Im done fitting it. I gotta talk her outta purple... I mean cmon yellow and purple? thats soo 90's