# Understanding the Dex Error System in Black Hole Mass Measurements

• Chronos000
In summary, the conversation is about the concept of "dex" in astronomy, which is a logarithmic unit used to express black hole masses. It is equivalent to the bel and is defined as 10x, with the notation now being used after the exponent. The name "dex" is a contraction of "decimal exponent" and there is a definition of dex on the website provided. The person is seeking clarification on the concept as they have not encountered it before in their research.
Chronos000

## Homework Statement

I've been reading various journal articles about black hole masses. The values given there are given by X +/- Y dex. I cannot find any literature on "dex" nor do the articles go into detail as it is evidently a basic concept that I've just never come across.

Could someone enlighten me?

from this website I got the definition of dex as:

dex
a logarithmic unit being used in astronomy. Originally, dex was a convenient function defined by dex (x) = 10x. But the notation is now being used after the exponent in expressions such as -.043 dex, meaning 10-.043. Thus 1 dex equals a factor of 10, making the dex identical to the bel. The name "dex" is a contraction of "decimal exponent."

http://www.unc.edu/~rowlett/units/dictD.html