@emerydaly - each Plug-in maintains its own version number that is independent of the core calibre version number. And each PI has a minimum calibre version number that it needs to install/run.
Current version number of QC plugin is 1.9.11
The minimum version of calibre on which that PI can be used is 0.9.29 (May 2013)
If you have calibre 2.5 you should be fine
BR
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