understanding the output of "apt-cache policy"

Question

I ran apt-cache policy sudo before and after installing sudo:

before install:

# apt-cache policy sudo
sudo:
  Installed: (none)
  Candidate: 1.8.5p2-1+nmu1
  Version table:
     1.8.5p2-1+nmu1 0
        500 http://ftp.se.debian.org/debian/ wheezy/main i386 Packages
#

after install:

# apt-cache policy sudo
sudo:
  Installed: 1.8.5p2-1+nmu1
  Candidate: 1.8.5p2-1+nmu1
  Version table:
 *** 1.8.5p2-1+nmu1 0
        500 http://ftp.se.debian.org/debian/ wheezy/main i386 Packages
        100 /var/lib/dpkg/status
# 

How to understand numbers 500 and 100? Are those some sort of status codes? In addition, what is the meaning of *** in front of the package version once it is installed?

Answer 1

500 and 100 are the priority numbers. To learn more about them, I recommend man apt_preferences. 500 corresponds to installable, 100 means installed.

From the man page:

If the target release has not been specified then APT simply assigns priority 100 to all installed package versions and priority 500 to all uninstalled package versions.

The *** just means installed, as far as I know. Once it has been installed, you see both 500 and 100, corresponding to the version in the archives and the locally installed version respectively.