FFF system

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The Furlong/Firkin/Fortnight (FFF) system is a humorous system of units based on unusual or impractical measurements. The length unit of the system is the furlong, the mass unit is the mass of a firkin of water, and the time unit is the fortnight.[1][2] Like the SI or metre–kilogram–second systems, there are derived units for velocity, volume, mass and weight, etc.

While the FFF system is not used in practice, it has been used as an example in discussions of the relative merits of different systems of units.[1][3] Some of the FFF units, notably the microfortnight, have been used jokingly in computer science. Besides having the meaning "any obscure unit",[4] the derived unit furlongs per fortnight has also served frequently in classroom examples of unit conversion and dimensional analysis.[5][6]

Base units and definitions[edit]

Unit Abbreviation Dimension SI unit Imperial unit
furlong fur length 201.168 m 220 yards
firkin fir mass 40.8233133 kg 90 lb[7]
fortnight ftn time 1,209,600 s 14 days

Notable multiples and derived units[edit]


One microfortnight is equal to 1.2096 seconds.[2] This has become a joke in computer science because in the VMS operating system, the TIMEPROMPTWAIT variable, which holds the time the system will wait for an operator to set the correct date and time at boot if it realizes that the current value is bogus, is set in microfortnights. This is because the computer uses a loop instead of the internal clock which has not been activated yet to run the timer.[8] In a further twist, the documentation notes that "[t]he time unit of micro-fortnights is approximated as seconds in the implementation."[9] Millifortnights (20 minutes, 9.6 seconds) and nanofortnights (1.2096 milliseconds) have also been used occasionally in computer science, usually to be over-complex, humourous, and obscure.[citation needed]

Furlongs per fortnight[edit]

One furlong per fortnight is a speed which would be barely noticeable to the naked eye. It converts to:

  • 1.663×10−4 metre per second, (i.e. 0.1663 mm/s)
  • roughly one centimetre per minute (to within 1 part in 400),[10]
  • 5.987×10−4 km/h,
  • roughly three eighths of an inch per minute, and
  • 3.720×10−4 mph.

The expression has also been used figuratively to mean at glacial speed (the pace or rate of progress is experienced as excruciatingly slow), as it is a realistic speed of some glaciers, about 14 m/day.

The speed of light[edit]

Another notable constant based on those units is the speed of light which is 1.8026×1012 furlongs/fortnight.


There is a British joke to the effect that when imperial units are abolished an exception will be made for the "British Standard measure of excess", namely the firkin, which will be retained but only used in twos as in "two firkin big", "two firkin small", etc.; and with "not" in technical terms relating to statistical significance such as "not firkin likely". This is playing off the fact that "two" and "too" are homophones, and in certain British accents, "firkin" sounds very similar to a profanity, thus the expression forms a minced oath.

In the FFF system, heat transfer coefficients are conventionally reported as BTU per foot-fathom [11] per furlong per degree Fahrenheit per fortnight.

Like the more common furlongs per fortnight,[4] firkins per fortnight have been used with the meaning "any obscure unit."[12]

See also[edit]

Notes and references[edit]

  1. ^ a b Stan Kelly-Bootle, "As Big as a Barn?", ACM Queue, March 2007, pp. 62–64.
  2. ^ a b Robert Slade, Dictionary of information security, Syngress, 2006, ISBN 1-59749-115-2, p. 122.
  3. ^ John D. Neff, "Imbedding the Metric", The Two-Year College Mathematics Journal, Vol. 14, No. 3 (Jun., 1983), pp. 197–202.
  4. ^ a b For example, in Jack G. Ganssle, The art of designing embedded systems, 2nd ed., Newnes, 2008, ISBN 0-7506-8644-8, p. 50.
  5. ^ Giambattista, Alan; Richardson, Betty McCarthy & Richardson, Robert C. (2004). College Physics. Boston: McGraw Hill. p. 20. ISBN 0-07-052407-6. 
  6. ^ Stephan, Elizabeth A.; Park, William J.; Sill, Benjamin L.; Bowman, David R. & Ohland, Matthew W. (2010). Thinking Like an Engineer: An Active Learning Approach. Prentice Hall. p. 259. ISBN 0-13-606442-6. 
  7. ^ The firkin of the FFF System is defined as the mass of an imperial firkin (9 imp gal) of water. The imperial gallon was originally defined as the volume of 10 lb of distilled water (weighed according to specific conditions). From this definition a density of 10 lb/imp gal is derived, giving the firkin of water a mass of 90 lb.
  8. ^ "microfortnight". Retrieved 2007-07-06. 
  9. ^ "HP OpenVMS System Management Utilities Reference Manual". Retrieved 2008-11-26. 
  10. ^ Indeed, if the inch were defined as 2.5454... cm, it would be 1 cm/min. "FAQ for newsgroup UK.rec.sheds, version 2&3/7th" (TXT). 2000. Retrieved 2006-03-10. 
  11. ^ The foot-fathom is a unit of area: 1 foot-fathom = 6 square feet.
  12. ^ Page-Jones, Meilir & Constantine, Larry L. (2000). Fundamentals of object-oriented design in UML. Addison–Wesley. p. 235. ISBN 0-201-69946-X.