Not sure where you were looking but this is taken directly from their website.
The ingenious Q90° quick center column system allows the user to move the central column from vertical to horizontal position in just seconds without having to disassemble the column."
If you go to this link http://www.bhphotovideo.com/c/product/548526-REG/Manfrotto_190CXPRO4_190CXPRO4_4_Section_Carbon_Fiber.html and select "Item Demo" you will be able to see a video that demonstrates what exactly the Q90 does. Just skip to the 1:17 mark.
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