The ratio of the diameter of the objective to the focal length of an optical instrument

The ratio of the diameter of the objective to the focal length of an optical instrument

Related Terms 
PLAN EQUATION
The mathematical statement that horsepower plan/33,000, where p mean effective pressure (pounds per square inch), l length of piston stroke (feet), a net area of piston (square inches), and n number of cycles completed per minute.

OVERDRILLING
The act or process of drilling a run or length of borehole greater than the corecapacity length of the core barrel, resulting in loss of the core.

OSTWALD VISCOMETER
A viscometer in which liquid is drawn into the higher of two glass bulbs joined by a length of capillary tubing, and the time for its meniscus to fall between calibration marks above and below the upper bulb is compared with that for a liquid of known viscosity.

ORIGINALDURATION
[INDENG] The initial estimate of length of time required to complete a given activity.

NYQUIST CONTOUR
A directed closed path in the complex frequency plane used in constructing a Nyquist diagram, which runs upward, parallel to the whole length of the imaginary axis at an infinitesimal distance to the right of it, and returns from jn to jn along a semicircle of infinite radius in the right halfplane.

NUSSELT NUMBER
A dimensionless number used in the study of forced convection which gives a measure of the ratio of the total heat transfer to conductive heat transfer, and is equal to the heattransfer coefficient times a characteristic length divided by the thermal conductivity. Symbolized NNu.

NAUTICAL CHAIN
A unit of length equal to 15 feet or 4.572 meters.

MODULAR STRUCTURE
1. A building that is constructed of preassembled or presized units of standard sizes; uses a 4inch (10.16centimeter) cubical module as a reference. 2. An assembly involving the use of integral multiples of a given length for the dimensions of electronic components and electronic equipment, as well as for spacings of holes in a chassis or printed wiring board. 3. An assembly made from modules.

MILLIMETER
A unit of length equal to onethousandth of a meter. Abbreviated mm. Also known as metric line; strich.

METER WHEEL
A special block used to support the oceanographic wire paid out over the side of a ship; attached directly or connected by means of a speedometer cable to a gearbox which measures the length of wire.

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