missing Launcher icon size slider

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http://askubuntu.com – In System Settings > Appearance in both Ubuntu and Ubuntu 2D, there is no icon size slider (in pixel units). How can I get access to the slider, which I know is visible in some installations of 12.04? Note this question is about the missing slider; not about changing the icon size. If I want to know how to change the icon size, I will post a separate question ;) If the slider is missing from Ubuntu 2D, that is not my concern since I don't use 2D. I only mentioned it for completeness. I need the slider for Ubuntu 3D. I am on a fresh installation of 12.04 with the updates to 2012 August (HowTos)