Carter BBD on my slant, help with float

mvh said

I'm looking at the Carter BBD manual, and the float adjustment for almost all applications is 1/4". The standard adjustment procedure involves flipping the carb upside down. But I can see how you could do it on the car, by holding it with your finger.

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yea in the old video , the guy pushes it down with finger, then measures. Gas is in there as well, so his fingers get gas on them. So what would be a good tool that I can set a 1/4 stop on and then rest it over the entire assembly? in video he is using what looks like a T square with some adjuster on the side??