A View from the Back of the Envelope envelope surfing
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These pages are about approximation, and some of the fun it enables.

You can always get back to this page by clicking on Envelope above.

Counting by powers of ten
"What order of magnitude is ...?" game
Counting to ten billion... on your fingers
Lots of dots and A million dots on one page
A dot for every second in the day (with a clock). New! 2001 Apr
Scaling the universe to your desktop
Meters in your hands
nano | micro | milli | meter | kilo | mega | giga | tera | peta
Constructing your own desktops.
How Big Are Things? New! 2001 Feb
How to simplify a number
by rounding , sometimes to an order of magnitude , sliding the decimal point , and using a number you can remember. Another example of simplifying is A ball's volume and area are 1/2 of its box's.
Exponential Notation is sliding the decimal point.
An Exponential Notation Meta Page.
Rounding to an order of magnitude and What is "order of magnitude"?
Scientific Notation is exponential notation plus conventions.
How to write and speak the exponential notation
Fermis Fermi Questions
Rough quantitative estimates about the world.
Talamo's Fermi Problems site - "What order of magnitude is ...?" game - A Pinocchio estimation game New! 2001 Feb - a mayonnaise story - landmarks - bounding - honesty - Why be approximate? - On Being Approximate
Scale Scale of some things
`Powers of Ten' scales
people , people seconds , volume , area , length , time , mass , energy , area volume-density , speed , volume rate , power
? Developing "deep" understanding
If you can't explain it to a nine year old...
( Picturing altitude above maps - teleportation - probing near space with a flashlight )
Getting a feel for big numbers - For children - Atomic bonding
Body Ruler
Measuring length with your body.
Measuring Angle & Distance with your Thumb
Books & some additional links.
Cosmic View: The Universe in 40 Jumps
A copy of the 1957 classic which inspired Powers of Ten.

Standing on the back of the envelope, one can see much of the universe. I have found it a vantage point of great power and beauty, but unfortunately one much neglected. It is my hope, in collecting these resources, to increase its accessibility, and to draw greater attention to it.
I welcome and appreciate your thoughts, your questions, and your contributions.

- Mitchell N Charity <mcharity@lcs.mit.edu>

Site alpha release 0.2 (1997.Aug.01)
Rewrote this page 1998.Mar.28.