I have/use the electronic guage. It has 2 ports. One goes to the reference cylinder the other to the the one being adjusted. On the adjustment port I have 2 aquarium air pump manifolds with 3 valves each. This way I can turn on or off whatever cylinder I wish to adjust. I have the 6 valves because I adjust some of my friends Honda wings and Valcs. This way you are always adjusting the carbs to the reference cylinder (#2 on our bikes), not 1 to 2, then 3 to 4, then 3/4 to 1/2. Works great for me. The gauge is like a MAP (manifold absolute pressure ) sensor on a car. The reference pulls a vacume on one side of the sensor and the adjustment port pulls on the other, the needle (or LED,s depending on make) shows the differance between the 2. This type of guage is for syncing carbs only. It is not, and does not give you a vacume reading, only the difference in vacume between 2 carbs.