That will teach me to read the thread and images properly.

OK - ECU gets one of it's load inputs from the TMAP sensor (temperature,manifold,absolute,pressure) ,which detects change of vacuum/pressure and air charge temperature in the intake so the ECU can calculate load and thus control fuelling and spark.

14.5psi is 1 bar absolute = atmospheric pressure (the air we breath). Which as Oldford posted can be checked with engine off key on. Also on WOT (wide open throttle) there will be no 'vacuum' on the intake so the manifold pressure should read approx. atmospheric pressure.