Flick: the flick unit for timing video displays
How small a slice of time might help coordinate the frame rates of different video displays? The proposed flick unit occupies just 1/705 600 000 second, or about 1.417 234 nanosecond. Its setting is video timing, where the purpose of the proposal is to coordinate frame rates across various display devices. The interval has a precise fractional definition and an approximate expression in nanoseconds. Beside familiar measures built around days and weeks, this tiny fraction belongs to a very different world: the timing of displayed images rather than the span of a calendar.
Video processing also gives the abbreviation fps one of its meanings: frames per second. That expression measures frames against time, while the flick unit names an interval of time itself. The same letters have other uses. In traditional measurements of speed or flow, fps can mean foot per second, written ft/s or ft/sec. A short abbreviation can therefore move between video and physical movement, depending on what is being measured. In the video setting, frames per second establishes the connection between the displayed frames and the second; the proposed interval approaches that timing through a fraction of the second.
The name flick also belongs to optical and communications engineering, where it measures spectral radiance rather than time. Radiance is power radiated per unit solid angle and per unit of emitting surface. Its value varies with wavelength. Spectral radiance expresses that variation as radiance per unit of wavelength span. In this use, a flick means one watt per steradian per square centimeter of surface per micrometer of wavelength span. These several dimensions make the engineering meaning quite different from a duration. The word and the symbol f are shared, but the measured quantities take separate paths.
Practical spectral-radiance measurements are typically expressed in microflicks. That smaller form belongs to the radiance meaning of the flick unit, with its power, surface, angle, and wavelength dimensions. Other optical measures describe different parts of the journey from light to an image. The f ratio of a camera or telescope lens measures its light-gathering power. It is the ratio of the focal length to the aperture, or effective diameter. An aperture may be reduced, or stopped down, for an exposure. Here the small letter f appears again, attached to a lens measurement instead of either radiance or elapsed time.
English speakers had a compact name for a much longer interval: the fortnight. It equals two weeks or fourteen days, and its name is a contraction of "fourteen nights." The word has been used since at least the 1100s. That naming history brings the measurement back to nights rather than fractions of a second. Both are units of time, yet their vocabulary grows around different activities. A fortnight carries the scale of a traditional English duration; the time meaning of the flick unit carries a proposed role in coordinating the frame rates of display devices.
Other old English measures began with the body. A fathom is the distance between a man's outstretched fingertips, and its name comes from an Old English word meaning "outstretched arms." The traditional length is two yards or six feet, approximately 1.829 meters. Comparable arm-span measures have appeared in many cultures since ancient times, including the Spanish braza, French brasse and toise, German klafter, and Japanese ken. The fathom was common in Saxon England and remained useful through the medieval era. Its history follows a physical reach that could serve as a measure of distance.
The finger had its own place in measurement. One traditional version represented the length of the middle finger from its tip to the joint attaching it to the hand. It equaled two nails or 4.5 inches. Another finger measure meant a digit, or three-quarters of an inch. Finger-width measurement was common in Anglo-Saxon England, and it survived informally after the twelve-inch English foot became established. These bodily measures gave lengths names rooted in familiar physical dimensions. Technical timing works with another kind of scale, using a defined portion of the second rather than a hand or an arm span.
Measurement names also travel into computing. The flops measures computing power as one floating point operation per second. Floating point numbers are stored with as many digits as a computer's design allows, whereas fixed point numbers have a fixed number of decimal places. In this terminology, a floating point operation is an arithmetic operation such as addition, subtraction, multiplication, or division of floating point numbers. Supercomputer power is measured in teraflops, meaning trillions of those operations per second. As with frames per second, the second provides the time basis; the activity being counted has become a calculation carried out by a computer.