Partial walk-around of the fuel
additive blender unit (FABU).
Picture 2 of 5.
There appear to have been several FABU design iterations; one, like this
particular FABU, had the full indicator on
the raised center
area, while others had the full indicator closer to the edge.
Below the black label (as it is mounted on the FABU) is the bleeder plug.
At left is the FABU's outlet port.