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.
Corrosion and build up on battery terminals can keep your car from starting, or cause your digital camera to fail when you want to take a shot of a special moment. No matter what kind of battery you have, your terminals can become corroded and poor conductors of electricity. Read on for tips on how to clean them up.