"Most accurate"
How did you prove that?
And does it even matter.
All you are doing is getting the idle to be the same on all carbs.
It all depends on the gauges you get and their rated accuracy. If I was a top end shop building full on racing engines, I could easily spend 3+ grand on a set of say ashcroft gauges guaranteed to 0.25% plus appropriate fittings and mountings. I would also be doing tunings all the way through the rev ranges because stable at idle might not mean stable at 6000+
Course with modern tech, I would probably build a data logging setup to monitor and combine it with a dyno and other instrumentation such as A/F metering, etc so that I could even monitor the pulses themselves.
The fluid type, such as the motion pro works by having the reservoir act as a counter vacuum. The calibration screw is nothing more than a piston. A restrictor in the hose keeps it readable. If I wanted a highly accurate and readable fluid type, it would end up being open atmosphere with a common reservoir with a low density fluid. This would set the head pressure all the same. Then, I would run fine tube up a wall, ideally rigid plastic or glass tube. Each tube would have a pair or sliders that would mark pulse high and pulse low. More sliders or recording camera to record various rpms.
On my 650, I adjusted the airbox boots to make the carbs syncronous at 4500.
