Percentage. Used to express a number as a fraction of 100. Using the percentage sign, %, 90 percent is expressed as 90%.

Permeability. Used to refer to the ease with which a magnetic flux can be established in a given magnetic circuit.

Perspective view. A drawing that shows a three-dimensional object (portraying height, width, and depth) as it appears to an observer. It most closely resembles the way an object would look in a photograph.

Phantom line. Composed of one long and two short evenly spaced dashes, indicates an alternate position of parts of the object or the relative position of a missing part.

Pictorial drawing. A drawing that is similar to a photograph. It shows an object as it appears to the eye, but it is not satisfactory for showing complex forms and shapes.

Pitch (aircraft maneuver). Rotation of an aircraft about its lateral axis.

Pitch (rivet layout dimension). The distance between the centers of adjacent rivets installed in the same row.

Pitch (thread dimension). The linear distance, measured parallel to the length of a threaded fastener, between corresponding points on two adjacent threads.

Pitch angle (helicopter rotor blade). The angle between the chord line of a rotor blade and the reference plane of the main rotor hub, or the plane of rotation of the rotor.

Pitch angle (propeller specification). The angle between the chord line of a propeller blade and the plane of rotation.

Pitch axis (aircraft axis). The lateral axis of an aircraft that extends from wing tip to wing tip and passes through the center of gravity. This is the axis about which the aircraft pitches.

Pitch distribution (propeller specification). The gradual twist in the propeller blade from shank to tip.

Plumb bob. A heavy metal object, cylinder- or coneshaped, with a sharp point at one end that is suspended by a string to produce a vertical reference line useful in aircraft measurements.

Positive number. A number that is greater than zero.

Potential difference. A difference in electrical pressure.

Potential energy. Energy that is stored.

Potentiometer. A variable tapped resistor that can be used as a voltage divider.

Power (exponent). A shorthand method of indicating how many times a number, called the base, is multiplied by itself. For example, in the number 43, 3 is the power, or exponent, and 4 is the base. That is, 43 is equal to 4 × 4 × 4 = 64.

Power. Power is the time rate at which work is done or energy is transferred.

Powers of ten. Also called scientific notation. It is a shorthand method of depicting very large or very small numbers.