Packing Fraction: The difference between the atomic weight in mass units and the mass number of an element divided by the mass number and multiplied by 10,000.

Parallax: The apparent displacement of an object as seen from two different points that is not on a line with the object.

Parallel Transmission: Transmission of data bits over different lines, as opposed to serial transmission.

Peak-to-Peak Amplitude: The amplitude of an alternating quantity measured from positive to negative peak.

pH: (A indication of the acidity or alkalinity of a solution.

PID Control: Control in which the control signal is a linear combination of the error signal, its integral, and its derivative.

Pointer: The needle-shaped rod that moves over the scale of a meter or dial.

Potential: The amount of voltage or change between a point and a zero reference point.

Potential Difference: The difference in potential between any two points in a circuit.

Potential Energy: Energy due to position.

Pontentiometer: A measuring instrument for measuring direct current electromotive forces.

Potentiometric Measurement: Comparing the unknown voltage with a known voltage from a calibrated potentiometer.

Precision: The closeness of agreement between randomly selected individual measurements or test results.

Pressure: Force exerted per unit area.

Preventive Action: Action taken to eliminate the causes of a potential nonconformity defect or other undesirable situation in order to prevent recurrence.

Primary Standard: A unit established by some authority or developed through practical application of a formula.

Probability: A measure of how likely it is that some event will occur.

Proportional Control: Control in which the amount of corrective action is proportional to the amount of error.

Psychrometer: A instrument for measuring relative humidity.

Pyrometer: A device for measuring high temperatures.