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Andrew Walkingshaw
              @covert, @timetric
             http://timetric.com/

The back of an envelope.
Enrico Fermi (1901-1954)
Trinity Test: July 16, 1945
10
     One.


 1



       10


            100

Orders of magnitude
Three rules:

   1. State your assumptions
     2. Justify your guesses
3. Be “dimensionally consistent”
Population of Chicago: ~5,000,000
 Households: 5,000,000 / 2 people ≈ 2,500,000
  Pianos: 5% of households ≈ 125,000 pianos

  Assume: each piano tuned once a year, taking
    ~2 hours: => ~250,000 piano-tuning hours
=> 250,000/8 hours per tuning day ≈ 30,000 days
  200 working days a year => around 150 tuners
And, actually:

290 “musical instrument repairers and tuners” –
  (source: Bureau of Labour Statistics, 2009)
Sanity check.
How big is the US newspaper
            industry?

value ≈ number of papers sold x
       revenue per paper

     npapers * $/paper = $total
Readers:

(number of potential readers x
     papers per reader)

          Revenue:

net price + ad sales per copy
How many papers are sold a year?

   225m people (aged 20-80)
  so around ~100m households
    maybe 25% buy a paper?

    => 25m daily circulation
~400 days a year, so 10bn a year
How much revenue per copy?

 Sales revenue: ~$0, more or less
       Revenue from ads ≈
revenue per ad x number of ads
            ≈ 2¢ x 100
          ≈ $2 per copy
So total US newspaper industry:
  ≈ 10bn papers x $2/paper
      ≈ $20bn per annum!
Actual number: $24.8bn print ad revenue
(2009: Newspaper Association of America)
Online:

    200m working adults
  200 working days per year
        4 pages each
        4 ads a page
$5 cpm per ad = 0.5¢ per view
=> 200m x 200 x 4 x 4 x 0.005
  ≈$3.2bn online ad revenue
Actual: $2.7bn (NAA, 2009)
(For comparison: Bloomberg LP do
    ~$7bn revenue per annum.)
When in doubt: check!
Thank you!

  http://timetric.com
http://withpretext.com

andrew@timetric.com
 @covert, @timetric

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The Back of an Envelope (at Ignite NewsFoo)

  • 1. Andrew Walkingshaw @covert, @timetric http://timetric.com/ The back of an envelope.
  • 4. 10 One. 1 10 100 Orders of magnitude
  • 5.
  • 6. Three rules: 1. State your assumptions 2. Justify your guesses 3. Be “dimensionally consistent”
  • 7. Population of Chicago: ~5,000,000 Households: 5,000,000 / 2 people ≈ 2,500,000 Pianos: 5% of households ≈ 125,000 pianos Assume: each piano tuned once a year, taking ~2 hours: => ~250,000 piano-tuning hours => 250,000/8 hours per tuning day ≈ 30,000 days 200 working days a year => around 150 tuners
  • 8. And, actually: 290 “musical instrument repairers and tuners” – (source: Bureau of Labour Statistics, 2009)
  • 10. How big is the US newspaper industry? value ≈ number of papers sold x revenue per paper npapers * $/paper = $total
  • 11. Readers: (number of potential readers x papers per reader) Revenue: net price + ad sales per copy
  • 12. How many papers are sold a year? 225m people (aged 20-80) so around ~100m households maybe 25% buy a paper? => 25m daily circulation ~400 days a year, so 10bn a year
  • 13. How much revenue per copy? Sales revenue: ~$0, more or less Revenue from ads ≈ revenue per ad x number of ads ≈ 2¢ x 100 ≈ $2 per copy
  • 14. So total US newspaper industry: ≈ 10bn papers x $2/paper ≈ $20bn per annum!
  • 15. Actual number: $24.8bn print ad revenue (2009: Newspaper Association of America)
  • 16. Online: 200m working adults 200 working days per year 4 pages each 4 ads a page $5 cpm per ad = 0.5¢ per view => 200m x 200 x 4 x 4 x 0.005 ≈$3.2bn online ad revenue
  • 18. (For comparison: Bloomberg LP do ~$7bn revenue per annum.)
  • 19. When in doubt: check!
  • 20.
  • 21. Thank you! http://timetric.com http://withpretext.com andrew@timetric.com @covert, @timetric