The Vebe test is described in BS EN 12350-3:2009 Testing fresh concrete – Part 3: Vebe test.
The apparatus is paced on top of a vibrating table. The fresh concrete is compacted into a conical slump mould. The mould is removed and a clear plastic disc is placed on the top of the concrete. The vibrating table is started and the time taken for the transparent disc to be fully in contact with the concrete (the Vebe time), is measured.
The main advantage of this test is that it is a dynamic test and can be used on concretes that are too stiff for a slump test.