# Units of dex^-1

1. Dec 11, 2009

### v0lD

Hi,

I've come across a number density expressed in units of Mpc^-3 dex^-1; I understand the Mpc^-3 but not the dex^-1. I know dex is some kind of log scale with n dex = 10^n but I'm not sure what dex^-1 means and was wondering if anyone could help.

Thanks!

2. Dec 14, 2009

### v0lD

3. Dec 14, 2009

### mathman

I got this from google (dex unit)

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."

4. Dec 14, 2009

### v0lD

Thanks - I'd found that same definition. But I'm still not 100% sure what the dex^-1 means. I mean, if 1 dex is 10 then maybe 1 dex^-1 is 0.1? But if it's just a constant factor of 0.1 to be applied to each data point then it seems pointless

I've seen Mpc^-3 dex^-1 used in plots in papers so I was hoping it was a common definition that someone would be familiar with.