Back-of-the-envelope calculation
A back-of-the-envelope calculation is a rough calculation, typically jotted down on any available scrap of paper such as an
A similar phrase in the U.S. is "back of a napkin", also used in the business world to describe sketching out a quick, rough idea of a business or product.[1] In British English, a similar idiom is "back of a fag packet".
History
In the natural sciences, back-of-the-envelope calculation is often associated with physicist Enrico Fermi,[2] who was well known for emphasizing ways that complex scientific equations could be approximated within an order of magnitude using simple calculations. He went on to develop a series of sample calculations, which are called "Fermi Questions" or "Back-of-the-Envelope Calculations" and used to solve Fermi problems.[3][4]
Fermi was known for getting quick and accurate answers to problems that would stump other people. The most famous instance came during the
Perhaps the most influential example of such a calculation was carried out over a period of a few hours by
Another example is Victor Weisskopf's pamphlet Modern Physics from an Elementary Point of View.[8] In these notes Weisskopf used back-of-the-envelope calculations to calculate the size of a hydrogen atom, a star, and a mountain, all using elementary physics.
Examples
In a video interview for the
During lunch with NFL commissioner Pete Rozelle in 1966, Tiffany & Co. vice president Oscar Riedner made a sketch on a cocktail napkin of what would become the Vince Lombardi Trophy, awarded annually to the winner of the Super Bowl.[10]
An important Internet protocol, the Border Gateway Protocol, was sketched out in 1989 by engineers on the back of "three ketchup-stained napkins", and is still known as the three-napkin protocol.[11]
UTF-8, the dominant character encoding for the World Wide Web,[12] was designed by Ken Thompson and Rob Pike on a placemat.[13]
The Bailey bridge is a type of portable, pre-fabricated, truss bridge and was extensively used by British, Canadian and US military engineering units. Donald Bailey drew the original design for the bridge on the back of an envelope.[14]
The
Upon hearing that the S-IV 2nd Stage of the Saturn I would need transport from California to Florida for launch as part of the Apollo program, Jack Conroy sketched the cavernous cargo airplane, the Pregnant Guppy.[16]
The Video Toaster was designed on placemats in a Topeka pizza restaurant.[17]
See also
- Buckingham pi theorem, a technique often used in fluid mechanicsto obtain order-of-magnitude estimates
- Guesstimate
- Scientific Wild-Ass Guess
- Heuristic
- Order-of-magnitude analysis
- Rule of thumb
- Sanity testing
- Fermi Problem
Notes and references
- ^ Brown, Bob (2011-07-19). "Napkins: Where Ethernet, Compaq and Facebook's cool data center got their starts". Network World. Archived from the original on 15 August 2019. Retrieved 2020-10-06.
Robert Metcalfe's early Ethernet diagrams from his days at Xerox PARC back in the early 1970s might be the most famous napkin sketches in the technology industry.
- ^ Where Fermi stood. - Bulletin of the Atomic Scientists | Encyclopedia.com (Archived)
- ^ Back of the Envelope Calculations
- ^ High School Mathematics at Work: Essays and Examples for the Education of All Students
- OCLC 13793436.
- ^ "Nuclear Weapons Journal, Los Alamos National Laboratory, Issue 2 2005" (PDF). Archived from the original (PDF) on 2018-12-29. Retrieved 2014-09-07.
- S2CID 111153288. Archived from the original(PDF) on 2015-05-25. Retrieved 2016-07-08.
- ^ Lectures given in the 1969 Summer Lecture Programme, CERN (European Organization for Nuclear Research), CERN 70-8, 17 March 1970.
- ^ Video of interview with Charles Townes; envelope mention comes about halfway in
- ^ "Vince Lombardi Trophy". ProFootballHOF.com. NFL Enterprises, LLC. Retrieved November 21, 2019.
- ^ Timberg, Craig (31 May 2015). "Net of Insecurity; Quick fix for an early Internet problem lives on a quarter-century later". The Washington Post. Archived from the original on 1 June 2015. Retrieved 4 January 2021.
As the prospect of system meltdown loomed, the men began scribbling ideas for a solution onto the back of a ketchup-stained napkin. Then a second. Then a third. The "three-napkins protocol," as its inventors jokingly dubbed it, would soon revolutionize the Internet. And though there were lingering issues, the engineers saw their creation as a "hack" or "kludge," slang for a short-term fix to be replaced as soon as a better alternative arrived.
- ^ "Usage Survey of Character Encodings broken down by Ranking". w3techs.com. Retrieved 2018-11-01.
- ^ Email Subject: UTF-8 history, From: "Rob 'Commander' Pike", Date: Wed, 30 Apr 2003..., ...UTF-8 was designed, in front of my eyes, on a placemat in a New Jersey diner one night in September or so 1992...So that night Ken wrote packing and unpacking code and I started tearing into the C and graphics libraries. The next day all the code was done...
- ISSN 0458-3035. Retrieved 2018-11-01.
He sketched the original design for the Bailey Bridge on the back of an envelope as he was being driven to a meeting of Royal Engineers to debate the failure of existing portable bridges
- ^ "This is not Arthur Laffer's famous napin" NY Times 13 Oct. 2017
- ^ Bloom, Margy (15 September 2011). "PilotMag Aviation Magazine | The Pregnant Guppy | The Problem: Logistics". Pilot Magazine. Archived from the original on 15 July 2011. Retrieved 25 April 2012.
[Conroy] listened to the conversations around him, then picked up a cocktail napkin and a ballpoint pen. And with the precision he'd learned during the brief months he'd attended engineering school many years before, he drew an airplane that had never been built, to carry a rocket that had never been launched, to take man to a place nobody had ever been before. Jack Conroy had just sketched the airplane that would become the Pregnant Guppy.
- ^ Reimer, Jeremy (18 March 2016). "A history of the Amiga, part 9: The Video Toaster". Ars Technica. Archived from the original on 18 March 2016. Retrieved 4 January 2021.
Montgomery suggested that Jenison meet his friend Brad Carvey, who had been working on projects involving robotic vision. The three of them got together in a pizza restaurant in Topeka and started drawing block diagrams on the placemats.