Stop in for a cup of coffee

Ben Drinkin said
Here's a fun guestion.. Need to hook up a tach to the bike to tune carbs. Mechanical tach is not detailed enough at low speed for the task. Question is, how does one hook up a tach to a 3 cylinder bike with 3 coils?

Can you hook up to one and then mentally divide and/or multiply?
Say it has a 6 cylinder scale, divide by 2?

Or use one of these multimeters with the inductive pickup and set for COP?