working with the carb upside down (I actually just pull the whole float assembly and do it. If you look a little, you'll see that there are some tabs on the assembly that work as a measurement point), and the float sitting on the needle under it's own weight. The distance from the "gasket surface" of the carb body to the highest point on the float itself is the "float height". Stock setting is 15mm.
Now, people will tell you that you have to be very careful to hold the carb at 45 degrees so that the float doesn't compress the needle spring. But, on the B4, the floats aren't heavy enough to do this, so I don't worry about it too much. In fact, I actually measure *down* from the cross bar on the assembly. That is, from the tube that ties the two ends of the float assembly together. That thing sits at 24mm from the gasket surface, so 9mm down from there is the stock setting.
I'll see if I can put together a picture.
A