Blood pressure is usually expressed in terms of the systolic pressure (maximum during one heart beat) pressure over diastolic pressure (minimum in between two heart beats) and is measured in millimeters of mercury (mmHg), above the surrounding atmospheric pressure (considered to be zero for convenience).
Corrosion on the terminals is due to hydrogen gas being released from the acid in the battery. It mixes with other things in the atmosphere under the hood and produces the corrosion you see on the terminals. Generally, if the corrosion is occurring on the negative terminal, your system is probably undercharging.
The knock sensor on the VE30DE is prone to corrosion of the terminals and harness connection. This is due to the harness weather seal getting brittle and cracking, allowing moisture to seep into the harness from the rear and corrode the terminals. This creates a poor connection and faulty voltage readings to the ECU.