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.
Cleaning Corrosion and Build Up in Car Batteries. Remove the battery cables from the battery terminals. Loosen the nut on each cable clamp. Remove the cable clamp from the negative terminal, marked with a -, followed by the clamp from the positive terminal, marked with a +. Reverse the procedure when replacing them.