### dex

(order-of-magnitude, decimal exponent)
(a number or factor's log base 10)

Dex (for decimal exponent) is a unit specifying an amount (e.g., a ratio) as the power of 10 that is relatively near that amount. Another widely used term for this is order-of-magnitude. A difference is that a dex is sometimes quoted as a fraction whereas an order-of-magnitude is typically rounded to an integer.

This is the same as the log base 10 of the number. For example, 100 could be described as 2 dex, or two numbers that differ by a factor of 1000 could be said to differ by 3 dex.

Within physics and astrophysics, the term dex is sometimes used, but order-of-magnitude is probably used more.

(mathematics,terminology,unit)
https://en.wikipedia.org/wiki/Scientific_notation#Dex
http://en.wiktionary.org/wiki/dex

Referenced by:
cosmic dust
dark energy
free-fall time
H-R diagram (HRD)
hyperfine structure
inflation
N-body problem
numerical analysis
planet formation
projected separation
stellar dynamics