Also the position of the GREEN Line in your image appears to be much more than 7.5mm down than when I have measured mine as seen below.
As a reference the head of the allen bolt shown in your image is approx 6mm high and the GREEN Line is almost level with that. ?
Scotch and I are saying the same thing. 7.5mm down from the "obvious" half joint, which is not the mating surface of the carb body/gasket/carb bowl since the carb body has a recess for the gasket and a spigot for the carb bowl to align. So maybe in other words "from the lower most machined edge of the carb body"