Barometer plugin does not work on 2.0.4-b4. Stand still at 0. Maximums have somehow correct values and colors (at least from my rough estimate).
I do not know weather this is plugin or piwik problem. Please move ticket to proper place in TRAC.
OS: CentOS 6.5
Plugin version: v0.5.1
That is not a core plugin, and thus not maintained by the team. Please create a ticket in the plugin repo on github: https://github.com/halfdan/piwik-barometer-plugin/issues