This is an adjustable platform. Such a platform is used, for example, to make sure that a gel electrophoresis cassette is level relative to the earth. A passage in a procedure description which I'm translating says that the gel caster (the two glass plates between which we will pour the solution) should be put on top of this platform, after which the platform is adjusted "using a level". The text describes a vertical SDS-PAGE procedure.
I wonder what such benchtop lab platforms are called. In my Russian text it is called "заливочный столик" (pouring table, casting table).