why does Chromium show version 18 even after an update?

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http://askubuntu.com – I updated Chromium in 12.04 with apt-get from the official repositories and chromium-browser --version say Chromium 20.0.1132.47 Ubuntu 12.04. but "About Chromium" from the browser itself say 18.0.1025.168 (Developer Build 134367 Linux) Ubuntu 12.04 why is that ? how can I update Chromium ? (HowTos)